That's great that you ordered the SI belt AND that it has helped you! In my experience now wearing the belt for about 3 or maybe 4 weeks, it helps, but it doesn't cure the problem. I'm continuing PT for my hip and can't emphasize enough how important to get a good PT and how difficult to find one. You should see weekly improvement.
Also, I think a lot of docs and PTs don't really know much about prolo but they seem to give lots of opinions. I kind of ignore whatever anyone says about prolo unless they have actual first-hand experience with giving prolo to athletes for the condition that I have. They theorize a lot but unless they have tried it, I don't buy it.
Check out caringmedical.com and read about prolo for SI joint. They are also on FB and post sometimes about patient stories. They could just be marketing hype--I still don't know--but I am prepared to try if I don't continue improving in PT.
My current PT (also just theorizing) says that she has read that prolo CAN help for SI joint problems. And my local doc (ortho surgeon for athletes) said the same thing. But again they also don't really have experience in this area. So I get hope from their comments but still not sure.
The bad news it sounds like for you is that insurance does not normally cover prolo . . . I've called several offices and asked for myself. If you don't need the PRP prolo, which is only for things like arthritis and labral tears, then you should be able to try the sugar solution . . . and prices seem to be about $600 for initial visit (includes consult), then $300 for follow-up visits. Sometimes people are cured with one or just a couple of visits, which is what I'm hoping would be true for me since my injury isn't severe. I think it would be worth saving to try to at least get one round of shots and see what happens IF PT doesn't work for you.
I'm actually planning a road trip from FL to Chicago (I hate flying!!) in a month or so IF PT doesn't continue to work. I need running in my life like I need air...