Having Lower Abdomal Pain It Hurts In My Stomach And

Having lower abdomal pain it hurts in my stomach and back, but it hurts in my butt when I try to sit down. It's happened a couple times over the last few years but after sex, so I had a pap done came back fine, but this time it was after a bowel movement. If I lay flat it relives the pain but if I stand up or sit I wanna cry.I had back surgery but dont think its related.