Is this just on one side? You definitely need to go see your doctor for an evaluation. There are several things that could be responsible for this. Examples include, endometriosis, gallbladder pain (although that is often upper quadrant pain, it 'can' radiate there), gall stones, kidney stones, IBS, a UTI, fibromyalgia, celiac disease, diverticulitis, https://www.healthline.com/health/abdominal-bloating-and-back-pain#irritable-bowel-syndrome-ibs The link doesn't look like it would apply but it does. Here is another with even more ideas. https://www.mayoclinic.org/symptoms/pelvic-pain/basics/causes/sym-20050898 When was your last physical?
I went and had a bladder ultrasound, CT scan of abdomen, and urine sample. All came back normal. At this rate, I am due for another attack tomorrow or Saturday!! I am getting worried!