Lemon:
First, I'm sorry you're having such a difficult time. I know it helps me to talk and share with others that understand. I'm glad you shared! As you most likely already know, each one of us are different and what helps one will not help another. That said, I will tell you a few minor things I have found helpful.
First, heat helps me. I use heating pads intermittently and moist heat seems to help the most with my SI joint pain.
Second: When it flares up, I know it's time to rest. I have to put my feet up. I have to alternate between moving and resting, and heat. No one thing or position works for me so I have to find the combination that will work. This is different according to which part of the body it is and the severity of the symptoms.
I have never had any luck with over-the-counter medications. I had a physician who would prescribe very mild opioids in the past. I found them to only alter the pain in a very minor way. I found them to not be worth the side effects and decided to avoid them. For no more relief they offered, I wanted to avoid the addiction issues.
Third: I tried multiple physical Therapist and was having no luck there as well. Until I located a PT from Poland. He trained and practiced differently from every PT I tried. Every time I visited this PT, I would have almost entire relief from my SI pain when leaving. Unfortunately, I found the pain would return in about one hour. The former multiple PT's I visited, I would never find pain relief, sometimes quite the opposite. I have no way of knowing if all Poland trained PT's practice the same way and may be able to offer you pain relief. Even short-lived relief was a nice change.
I hope you may find something here that will prove useful. One thing I admire, are people that get hit by so many things, and never give up. I guess that pretty much sums up everyone here. We learn from each other and keep moving forward. Wishing you the best and hoping you find something helpful.