I've always been a fan of massage therapy and very much believe in the benefits it brings. For any ailment, increased blood flow is the best. Things like massage therapy, acupuncture, bfst, ultrasound, etc. So whether it is your hip flexor or you SI joint, focus on things that help with the circulation. It's so important. With what your describing and how it goes down to your hamstring, I think it seems more like your SI joint. Here's some great info on how important good circulation is for any injury. Improving Blood Circulation