I have pain on my right side coming from my pelvis area. It happens right before my cycle starts and gets worse with cramps. What's causing this?

Sacroiliac joint. 20's with right pelvic premenstrual pain likely has sacroiliac joint, SIJ, subluxation/ligamentous stretch due to hormone Relaxin, which is secreted at this time in the menstrual cycle; evoking pelvic ligament laxity. Weight loss, yoga, and SIJ belt might be therapeutic. A negative pelvic ultrasound might help to solve the differential diagnosis. .