I have had teeth infections & swelling in past & have gingivitus. But recently I began experiencing something different - a dull aching, throbbing & metallic taste on left side (top and bottom teeth). The teeth and gums are not swollen or sensitive to touch. Pain is increased after eating & drinking (coffee especially, it seems) - not necessarily hot or cold food/drink. I have amalgam fillings and am wondering about mercury poisoning.
This could be due marginal breakage of your amalgam filling, which may lead to sensitivity and mild throbbing pain, you may need to take x-ray of the particular tooth and check for any pupal roof damage, which may occurs in long-standing amalgam filling.  The treatment could be either new filling or needs root canal treatment. The history also shows gingivitis, so oral prophylaxis with mouth wash will help u.