Sex followed by cramping, tightening, and back ache..

Jas

I’m 37 weeks and 5 days and my child’s father had sex and 20 mins later I started feeling cramping, tightening, and back aches... It’s hurts more when I lay down and not as much when I sit up.. Have anyone else ever felt like this!? I know it might not mean as much dealing with labor but, I’m still curious as to, have anyone had sex which led to sex!?