If your fillings are silver colored they are mercury amalgams. The only other types of fillings are white plastic. So yes, you have a lot of amalgams. I know someone with 16 and he is very sick. I am not a doctor but it sounds like this is the problem. No more tuna!! Use protein powder. Tuna is high in mercury and you really don't want to add to what you already have in your body. I can say that I have always had low level poisoning as you describe it, but it started to get worse at your age. I am 33 now and pretty functionless.
Tread cautiously with your doctor. Most of them do not beleive that amalgams can poison you. You can try to ask to be tested for "heavy metals". You may need to find a naturpathic or holisistic physician if yours won't cooperate. Or have your doc send you to a specialist in enviornmental medicine. This message board is a good place to start to get the info you need to get better.