I have had problems with my sacroiliac ligament for 18 months. nothing seems to make it better and am considering prolotherapy. any thoughts?

Yes: Unless you had a significant pelvic trauma ( fracture ) it is unlikely your pain is from this region and the prolotherapy, if done , would work if at all like a placebo effect. You need a specific evaluation by a spine specialist to find the cause of this chronic pain. If in the rare case it was related to the si region, a block would first be done to confirm this and then rhizotomy done.

Try it: I would recommend a formal course of physical therapy along with anti-inflammatory medications. A subsequent pain management consultation is warranted. Possibly an si joint injection may help. Try prolotherapy and see if it works that could be another option for you.