Horrible lower back pain

Hey guys so I’m 40 weeks 5 days and last night I had sex for the first time in months and he came inside me also I walked a lot during the day. Sorry I’m a ftm so idk if this is normal. I started having horrible lower back pain a couple hours after and I started feeling pain inside like a wave idk if those were contractions or not it hurts to walk like my butt hurts a lot a lot idk what to do Im In so much pain.