Yeah, it's hard to say what is doing it. It could be mercury directly (allergy/toxicity), or mercury indirectly by it's action inside you. Same for candida yeast and parasites as you mentioned. Both of them feed off sugars in the diet and high carbs (fruit, potatoes, beans/peas, honey, milk, sugar) and yeasty foods can cause problems as well. I'd stay off these things completely. High yeast apparently can methylate mercury and make it more toxic. High yeast can also allow mercury to do even more damage due to weakening the body, overloading the gut and liver with yeast alcohols/toxins. In fact candida alone, can cause so much misery that some have been known to commit suicide from candida. THe toxins from it affect the brain. So it's no small issue.

You could try upping your fat intake for sure. I get the oil straight and everytime I have my yoghurt, Im mixing in a teaspoon of flax oil in it. This might be 3 times a day or so. And on top of that Im having butter in my meals and when I cook I have butter and olive oil. Salads, I have olive oil. I even eat fat on the meat with the meat. It may sound "bad" because of the bad press fat gets, but these animal fats are doing fine with me and are advocated by the likes of Dr weston Price who has studied the healthiest cultures/specimens around the world for many years.

But again, I am eating very healthy foods too. Also Im sure the cultures Dr Price studied were probably much more active than most of us and burned things off sufficiently.

Fat and proteins are also advocated by Dr Hal Huggins (one of the mercury pioneers). He mentions that in his book and recommends steering clear of caffeine, sugar, etc and consuming enough meats, butter, etc. I would say balance that out with vegetables! Fruits are great as well, but for someone with high yeast, it may feed on that too much.

anyway sorry for the lengthy response!