Katrina,
I had spotting and cramping with both of my pregnancies and I have 2 little ones right here. In my second pregnancy, I didn't just spot, I BLED, a lot, for a long time (maybe 3 months)....and they couldn't figure out what was wrong. Turns out, nothing was wrong, the baby was totally fine....and these things just happen.....totally unexplained.
I will keep you in my thoughts and hope that this is the case for you.
Susan