I, too, was diagnosed with MTHFR after finding out I had had two small strokes. I recently learned it can be the cause or contribute to miscarriages (I had one in between having my two girls). If you are homozygous for the condition, it is imperative you stay on a daily regimin of Vitiman B, folate and aspirin. Consult your doctor on the levels you should take. I also recelty learned that this condition can contribute to anxiety and depression. As far as all of your other concerns, I would consult a geneticist and a reproductive endocronologist. Finally - my OBGYN told me I could NEVER be on any hormonal therapy.
I would definitely go for the lap. It will give a lot more clear picture of what's going on in there. I wish I could tell you why it happens so easily sometimes then not again. The same thing happened to me. I got pg with new dh on the 1st try. Miscarried at 12wks with a torn placenta. It's been 2yrs since then. The only explanation they have given is that I was "lucky" the one time. Yeah, real lucky, lol. I hope they get to the bottom of it soon for you!