What could be causing bad pain in the lower abdomen in the middle? "feels like my stomach muscles stretching, not cramps. Has happened all day, now worse

?Appendix,bladder, Gastroenteritis, constipation, ovarian ectopic pregnancy, bowel ischemia etc. Also depends upon other symptoms, gender and age, suggest you see your dr. Or go to an er asap unless pain subsides.
Maybe bladder. A painful stretching, non-crampy sensation in the lower abdomen near the midline can be caused by an overstretched bladder or bowel, a urinary tract infection, or even possibly an ovarian cyst or other reproductive organ problems. See a doctor if the pain continues > 24 hrs. If more questions, a urine test and exam of your abdomen don't show a clear answer, a pelvic exam may also be necessary.