Yes, you should get it checked nanny, Protein C and S are something the Professor was talking about gets affected in pregnancy and is an issue for those with clotting problems.
I'm on Clexane purely because that's what I was started on during the IVF cycle with Serum; I think Fragmin is probably more widely used in the UK.
I do take 75mg aspirin as well, yes, and I was told to carry on taking it - it has a different effect on clotting than Clexane does.
I ended up with the Head of Haematology because I asked my consultant if I could stop taking Clexane at 12 weeks (the standard time IVF patients with Serum stop taking it). Serum had advised if you have blood clotting issues to check with your consultant before stopping it, so I did. She didn't have a clue, one of her registrars spoke with one of the haematology team at the hospital who wasn't well versed enough in MTHFR to advise either way, so my consultant then said it should be referred to the Head of Haematology, as he's extremely experienced. And he is, thankfully!
Ask anything you like, I don't mind :) I only know that I researched this when I was first diagnosed, and ascertained that it is potentially a whole lot more serious than Mr S was prepared to believe, so started taking l-methylfolate (instead of the folic acid Mr S said to take) along with the methylcobalamin form of B12 and high-dose B6. Which all turns out to be have been completely correct, according to the Prof.