Julie - I have the same. As your embryos have been implanting I wouldn't worry too much. Basically there is a chance you don't process Folate properly so as the girls said before - just buy the Megafol 5mg as opposed to the .5.
Yes and next round you will most likely be put on Clexane - but with a lead up of asprin. Asprin stops when clexane starts. Mind you my FS didn't put me on asprin at all - just clexane.
MTHFR can cause some clotting issues - hence can sometimes hinder implantation. They use the asprin/clexane to ensure smooth uterus and not clotting.
I know you are upset you weren't told but at least you now know it's really not too serious.