ON THE OTHER HAND - and what I'll say is true ONLY if there is a valid reason to even consider heavy metal poisoning (like Amalgam fillings or lots of certain types of sea food in the diet):
All those endless tests are A LOT more expensive than simply TRYING to see what happens with a chelator. DMPS is "mostly harmless" (using a Douglas Adams quote). I'm not going to waste space on the endless discussion of DMPS and DMSA, to be honest: if you are too afraid then I could not care less, my time is too valuable to waste it in these forums. I just felt I had to say something. Myself, I doubted the "it's all caused by the Amalgam (i.e. the mercury mostly)" for 1-2 years while getting DMPS regularly, and the doctor who gave them (but he did!) also said similar things to what you said and checked LOTS of other things (all for naught). I have made HUGE improvements, after 2 years there was no more doubt for me and for my doctor that it was the mercury.
But back to the beginning: A 100% (or even 50%) correct analysis of whether or not heavy metals are the cause IS IMPOSSIBLE. Maybe in a hundred years. Almost ALL treatments in medicine are "let's try and see if it helps", for some reason whenever heavy metals are suspected and the chelators used to treat them are A LOT better tolerated than e.g. Antibiotics there's an outcry "don't try this, first make 10000 other tests".
So, just try it. Your symptoms ring more than just one bell, on the other hand if you didn't have any direct contact with heavy metals yourself, only through your mother, well, I've no idea how well-founded the hypothesis that the mother gave you significant amounts of mercury is.
Anyway, you should understand that, regardless of all the "great" advice especially here in these forums, your best chances are to "keep moving". TRY stuff. Nobody knows! I've gone through my fair share of medical and biology lectures. It is amazing how much we know, I actually cried occasionally because I was so awed. Yet we know NOTHING, really, when it comes to solving problems such as yours, it's a lot of blind guessing. The worst part, even if something actually helps you don't know if what was treated was the actual cause or if only the symptoms were suppressed. A lot of people feel better when doctors give them a "name" (of a disease) - but doctors have LOTS of names for "diseases" that they have no idea what caused them, and even less about how to cure it (how often is the only advice they have to simply cut something out of your body?).
So if you want to know if heavy metals, mercury, could be the cause, try DMPS and/or DMSA (DMPS is **MUCH** more effective). Using it just once won't give a definite answer (unless it already causes improvements), you may need 3-5 treatments before seeing/feeling an effect. However, chelators are benign, whatever people may say. I would be MUCH more concerned about the money and time for all those tests that some poster here proposes (the only reply I read and it cause me to reply, usually I keep my mouth shut these days) - they are all non conclusive whatever the result, none of them establish a cause.
I feel really bad about giving any advice, because while I cured myself (where 1 professor and >10 doctors failed again and again, and the one university doctor who is left doesn't really know but is helpful nevertheless; but I beat them all not just a little but by several orders of magnitude as far as the size of my success can be measured in any way) I spent LOTS of resources (money but mostly time), definitely not an easy path, and of course I have no idea if any of it really helps others. It's just that when I read that lengthy reply here that you should not consider heavy metals so quickly and first do tests a, b, c, d,.... I jumped. Those are all expensive and time consuming, and even if you get a result it doesn't help at all, because none of those tests establishes a CAUSE, and you already know you have problems.