Perhaps it's that sp something or other. Sorry I can't remember what it's called, but I had it with DS2, when your pelvis hurts. I wore a belly band support, that really helped. Hope you stop having cramps soon.
I get them in all of my pregnancies. I am almost 7 weeks with DC4 and getting them this time round too.
With my 1st pregnancy I was sure I was going to miscarry as they were so bad, no doctor oculd ever explain why they were so bad but everything turned out fine and they stopped completely by about week 14.
Hope this helps, I could never find anything online about cramping in pregnancy and I used to worry myself sick!