I am having defininte sacroiliac pain. It started as a minor irritation in the right buttock and grew over a period of weeks. The transition from standing to sitting started the more major pains, progressing to the transition from sitting to standing, then maintaining a sitting sitting position, then standing/walking, and finally to where the pain was not relieved even with laying down. Last week, I had a guided injection into the SI joint. This helped somewhat for a few days. The more significant pain seems to be returning. I do not recall any injury that may have caused this pain. I am not pregnant. The doctor says I am too young for it to be arthritis (though I'm not sure I believe this - I'm 38). What are other causes of SI joint pain???