My doctor actually works with many patients who have mercury fillings in their teeth, and they have the same problems as you! What she has advised them to do is to go to a dentist who does not use mercury fillings, and TAKE OUT the mercury and re-fill them with alternative healthy substance. I have spoken to one patient at the office, and she has told me that her health had drastically changed from taking out the mercury fillings! If you're in the UK, I dont know how dentistry is there, but I live in USA near New York City and there are a lot of dentists in this area who are going holistic. If you ever travel here and cant find a dentist in the UK, go to one here...no?
ANyway, these are just my suggesstions. I hope you start to feel better.