Ectopic pregnancy is another serious possibility here.
Your symptoms can be caused by bladder infection commonly --sometimes urinary symptoms may not be present.
Kidney stone is another possibility--given the fact her pain is radiating to back and feels like bruise. Obstructing stone can cause such symptoms.
Uterus inflammation due to hormone changes, endometriosis, Fibroid, or bacterial infection are another possibility.
Ovarian cysts next cause-- especially a large one which may be rupturing.
Intestinal infection or colitis or diverticulitis - usually constipation or diarrhea also present.
You can try over the counter Naproxen 2 tabs twice daily to see any improvement.
If not, you will need urine analysis, pelvic ultrasound sooner than later.
Please go to the local hospital