Entry Pagination - Group by Current Category and Order by Post Date
Using the pagination helper might be a cleaner way to achieve your desired results. It would go something like this:

{% paginate craft.entries.section('news').order('postDate').relatedTo({targetElement:categoryId}).limit(5) as entries %}
    {% for item in entries %}
        {# your item code goes here #}
    {% endfor %}
    {% if paginate.prevUrl %}
        &lt;a class="button left" href="{{ paginate.prevUrl }}"&gt;Previous&lt;/a&gt;
    {% endif %}
    {% if paginate.nextUrl %}
        &lt;a class="button right" href="{{ paginate.nextUrl }}"&gt;Next&lt;/a&gt;
    {% endif %}
{% endpaginate %}


By using the relatedTo({targetElement:categoryId}) param you will stay in the same category as you paginate entries. This pagination helper handles the urls.  So we are just accessing the paginate.prevUrl &amp; paginate.nextUrl variables provided by the helper.  All you need to do is make sure the categoryId is set to the category you need and set the limit to the number of items to paginate by.

--

For your particular setup I would use two templates.  One for the News landing page and one for the category landing. The news landing page will paginate all News entries. 

Once a category is clicked and now uses the template specified in the category setup page, you will limit paginated entries to the current category.  The variable category is reserved for those templates so you can access anything variable associated with the current category you are on. You will only notice slight difference between the two. The Category Template adds the relatedTo({targetElement:category.id}) criteria in addition to setting the active category class.

Here are both templates.

News Landing Template

{% set title = entry.title %}
{% set description = entry.body | striptags %}

{% extends "_layout" %}

{% block content %}

  &lt;div class="heading"&gt;
    &lt;h1&gt;{{ newsHeader.header }}&lt;/h1&gt;
  &lt;/div&gt;

  &lt;div class="filter-bar news"&gt;
      &lt;div class="container"&gt;
        &lt;ul class="largenav"&gt;
            &lt;li&gt;&lt;a href="/news"&gt;All&lt;/a&gt;&lt;/li&gt;
            {% for topic in craft.categories.group('newsCategories') %}
              &lt;li&gt;
                &lt;a href="{{ topic.url }}"&gt;{{ topic.title }}&lt;/a&gt;
              &lt;/li&gt;
            {% endfor %}
        &lt;/ul&gt;
        &lt;div class="select tinynav"&gt;
            &lt;a href="#" id="select-toggle"&gt;All&lt;/a&gt;
            &lt;ul&gt;
                &lt;li&gt;&lt;a data-value="{{ siteUrl }}news" href="#"&gt;All&lt;/a&gt;&lt;/li&gt;
                {% for topic in craft.categories.group('newsCategories') %}
                  &lt;li&gt;
                    &lt;a href="#" data-value="{{ topic.url }}"&gt;{{ topic.title }}&lt;/a&gt;
                  &lt;/li&gt;
                {% endfor %}
            &lt;/ul&gt;
        &lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;

    {% paginate craft.entries.section('news').order('postDate').limit(5) as entries %}
      &lt;ul class="wrapper newspage"&gt;
        {% for item in entries %}
          &lt;li class="news-item"&gt;
            &lt;h1&gt;&lt;a href="{{ entry.url }}"&gt;{{ entry.title }}&lt;/a&gt;&lt;/h1&gt;
              &lt;h5 class="meta"&gt;{{ entry.postDate|date("F j, Y") }} &amp;nbsp;|&amp;nbsp;

                  {% if entryCategories | length %}
                    {% for topic in entryCategories %}
                      &lt;a href="{{ topic.url }}"&gt;{{ topic.title }}&lt;/a&gt;
                    {% endfor %}
                  {% endif %}
              &lt;/h5&gt;
            &lt;p&gt;{{ entry.body }}&lt;/p&gt;
          &lt;/li&gt;  
        {% endfor %}
      &lt;/ul&gt;
      &lt;li class="news-item"&gt;
        {% if paginate.prevUrl %}
            &lt;a class="button left" href="{{ paginate.prevUrl }}"&gt;Previous&lt;/a&gt;
        {% endif %}
        {% if paginate.nextUrl %}
            &lt;a class="button right" href="{{ paginate.nextUrl }}"&gt;Next&lt;/a&gt;
        {% endif %}

        &lt;div class="clear"&gt;&lt;/div&gt;
      &lt;/li&gt;
    {% endpaginate %}
  &lt;/ul&gt;

{% endblock %}


Category Template

{% set title = entry.title %}
{% set description = entry.body | striptags %}

{% extends "_layout" %}

{% block content %}

  &lt;div class="heading"&gt;
    &lt;h1&gt;{{ newsHeader.header }}&lt;/h1&gt;
  &lt;/div&gt;

  &lt;div class="filter-bar news"&gt;
      &lt;div class="container"&gt;
        &lt;ul class="largenav"&gt;
            &lt;li&gt;&lt;a href="/news"&gt;All&lt;/a&gt;&lt;/li&gt;
            {% for topic in craft.categories.group('newsCategories') %}
              &lt;li&gt;
                &lt;a href="{{ topic.url }}" {% if category.url == topic.url %}class="active"{% endif %}&gt;{{ topic.title }}&lt;/a&gt;
              &lt;/li&gt;
            {% endfor %}
        &lt;/ul&gt;
        &lt;div class="select tinynav"&gt;
            &lt;a href="#" id="select-toggle"&gt;All&lt;/a&gt;
            &lt;ul&gt;
                &lt;li&gt;&lt;a data-value="{{ siteUrl }}news" href="#"&gt;All&lt;/a&gt;&lt;/li&gt;
                {% for topic in craft.categories.group('newsCategories') %}
                  &lt;li&gt;
                    &lt;a href="#" data-value="{{ topic.url }}"&gt;{{ topic.title }}&lt;/a&gt;
                  &lt;/li&gt;
                {% endfor %}
            &lt;/ul&gt;
        &lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;

    {% paginate craft.entries.section('news').order('postDate').relatedTo({targetElement:category.id}).limit(5) as entries %}
      &lt;ul class="wrapper newspage"&gt;
        {% for item in entries %}
          &lt;li class="news-item"&gt;
            &lt;h1&gt;&lt;a href="{{ entry.url }}"&gt;{{ entry.title }}&lt;/a&gt;&lt;/h1&gt;
              &lt;h5 class="meta"&gt;{{ entry.postDate|date("F j, Y") }} &amp;nbsp;|&amp;nbsp;

                  {% if entryCategories | length %}
                    {% for topic in entryCategories %}
                      &lt;a href="{{ topic.url }}"&gt;{{ topic.title }}&lt;/a&gt;
                    {% endfor %}
                  {% endif %}
              &lt;/h5&gt;
            &lt;p&gt;{{ entry.body }}&lt;/p&gt;
          &lt;/li&gt;  
        {% endfor %}
      &lt;/ul&gt;
      &lt;li class="news-item"&gt;
        {% if paginate.prevUrl %}
            &lt;a class="button left" href="{{ paginate.prevUrl }}"&gt;Previous&lt;/a&gt;
        {% endif %}
        {% if paginate.nextUrl %}
            &lt;a class="button right" href="{{ paginate.nextUrl }}"&gt;Next&lt;/a&gt;
        {% endif %}

        &lt;div class="clear"&gt;&lt;/div&gt;
      &lt;/li&gt;
    {% endpaginate %}
  &lt;/ul&gt;

{% endblock %}