What could cause painful intercourse, stomach cramps, and lower back pain?

Many things: Could be gyn or non gyn. Could be fibroids, endometriosis, scar tissue , infection, ovarian cysts. Non gyn could be interstitial cystitis. Could be bowel problems. All these organ systems could be causing pain. You should see your gyn for a work-up which would include an exam, blood work, ultrasound to start off with. You may need a laparoscope or referral to another specialist, so please see gyn.