I had something similar. The orthopedic guy sent me in for some vigorous PT. It hurt, but I really worked at it .....and I only got worse! After about a month and some steep copays, I quit and just tried very gentle movements on my own. It continued to get worse for a while, then just stayed stiff for a long time before gradually, over many months, getting somewhat better. The doc didn't give me a name for the condition, but the whole cycle of getting worse, then staying very stiff but hurting less, and then finally improving, followed the descriptions I found online for "frozen shoulder"...if that's even a real thing.
Now I'm going in to another doc to see if he can do anything for my "achilles tendonosis". From the research I've done, it's another tricky situation with no one "gold standard" of treatment. Still, it would be nice to be able to walk without a limp. It would really help my MA if I didn't hurt all the time. Running is out of the question, but at least being able to take long, brisk walks again would be great and help me lose a few pounds too!
Anyway, I really hope your PT does the trick. Let us know for sure!