28 weeks pregnant and severe pains after sex?

so my husband and i had sex...and right after i was in really bad pain!! in my lower stomach/ pelvic area...and the pain will go in my lower back too..and i feel as if i have to poop..but i know im not constipated..never have been throughout my entire pregnancy, and i went like twice already today..well i waited an hour to see if the pain would ease up..and its not!! its been a little over an hour and it hurts really bad..im not sure what contractions feel like because this is my first baby..but i will feel as if my entire bottom stomach or a part of it will just tighten up and get hard and it hurts really bad then it eases up but im still in pain after it happens..like an uncomfortable feeling..then it will hurt worse for a few more minutes..lol..its hard to explain and i apologize..but there is no bleeding or anything and my water hasn't broke or anything but these pains are almost unbearable it seems..i can't even get up or move around in bed because it just hurts so bad..im drinking water and laying on my left side..still hasn't seemed to help