I think you r right regarding your diagnosis. Lets do a X-ray first to see whether associated with sacroilitis or not.(X-ray both pelvis including sacroiliac joint AP VIEW). In the meantime you can use tab. Chymoral
forte with tab. Rantac
(150) two times a day for 3 days at least. If you allow we can talk personally for further management protocol after X-ray. Avoid sitting on hard surface and avoid blunt trauma.