What could be the cause of my sacroiliac joint problems?

Sacroilitis: You may inflammation in the joints called sacroilitis. Try Ibuprofen or Naproxen for relief. If no improvement get an x-ray to check for arthritis.

Injury: If you are male, i vote for mechanical injury, & extreme sports are a veritable breeding ground for sacroiliac joint (sij) injury, i.e., ligament injury, ligment laxity, and sij subluxation (a partial & self-reducing type of dislocation). In my clinical experience skateboarding is greatest cause of sij injury. In females multiple childbirths and joint hypermobility syndrome are primary causes.