31 weeks now cramping?

So I'm 31 weeks today, it's my birthday so my husband and I had sex, we've had sex pretty much weekly if not daily my whole pregnancy but today is different. I'm now having period like cramps, back pain and some more tender pains on my left hip area.. is this normal? I know cramping after sex can be but this is different then what I've had. Baby girl is moving and kicking normally, if not just a little more then her usual night time crazy fest. This is my first so I just want to make sure before I call my midwife, since it's 1am here. Thank you ladies!