Hi-- you should be on progesterone which would prevent AF even if you weren't pregnant. For reference, I was on 200mg suppositories 3x/day. At a minimum, whether you're pregnant or not, I'd insist on having your Dr check your progesterone levels *now* b/c if they are low they can correct it now or, if you're not pregnant, for the next cycle. I did this b/c I was having some cramping and sure enough, I wasn't absorbing the suppositories well enough... it's worth asking the question at least...
If it helps, I had some spotting which did turn out to be implantation bleeding and made my Dr do the pregnancy test early -- sounds like you're going tomorrow so you'll know soon. Hang in there and keep us posted.
Many women have heavy bleeding following ivf (including myself) and your dr will want you to take progesterone till a blood test proves it's a negative. I am so sorry about a negative EPT :(