I have bursitis in,most parts of my body, luckily, never frozen shoulder.
You think perhaps when you get back to activity you over did it? It never fails when I forgot I should slowly ease back into my stretching. The physical therapy I went once worked me out so hard and did me more harm because they didn't understand FMS, specially not ME/CFS.
Sometimes, I use heating pad, in conjuction with a warm bath with epsom salt. It kind'a helped.
Feel better soon.
Kit
I have been to Physical therapy for several problems, and it always hurts more before it gets better. You should tell the therapist that what they are doing is hurting too much.
I do get swelling and pain in my biceps and was told this is from fibro. But I can't say for sure in your case. Were you lifting weights? Lifting even light weights makes my arms and sometimes my thighs swell.
I've never experienced this, but I do know that a "frozen shoulder" is very common in people who have Th1 illnesses (autoimmune diseases, fibro, CFS, etc.)