Need help about giving relationships in database design
Try something like this

user (user_id(pk), user_name)

post (post_id(pk),user_id(fk), post_content)

comment(comment_id(pk),post_id(fk),user_id(fk), comment)

likes(post_id(fk), user_id(fk) status)


In status column in likes table you can save it as like or unlike can be tinyint field with 

NULL - Default value
True - Like and False - unlike(if you have unlike option)