If you are a negative blood type you need an RH shot. That is what happened to me.
I had cramping and spotting A LOT at first and now I'm 14 weeks and all looks good! Do you know your blood type?
Your uterus can be a big reason for cramping. Your body is making room for that little one so there's going to be some cramping. I wouldn't worry about it unless it becomes very strong and is accompanied by bright red bleeding.