What Causes Frozen Shoulders When Diagnosed With Biceps Tendinosis?

Question: I have had biceps tendinosis for about 3 months. I have recently started physical therapy. I am wondering if it is normal and OK that I experience some pain during the exercises and this lasts at least 24 hours. It’s hard to tell if I should call it pain or soreness. It might be both. It is not constant. It is only on certain movements and it might be like a 3 in intensity out of 10. If I take a day or two off, the pain is better. I don’t know if the pain means I’m damaging the tendon or if I need to keep doing the exercises in order to heal the tendon.
Here is the longer version of my story. Thirteen months ago (early October 2016), I fell down the stairs. My arm awkwardly stopped my fall and I hurt my shoulder. At the time, I was diagnosed with shoulder impingement. Physical therapy was making the arm (shoulder and biceps) hurt. So I stopped physical therapy and tried to completely rest my arm for a month. I tried to do everything only with the healthy arm. This was a mistake, as I developed frozen shoulder.
By May (7 months after the fall), the frozen shoulder was about 90% healed and I was doing well. From August to mid-October, though, I overused my arm though. My major hobby is photography. I did way too much photography and driving, and the biceps tendon started to become sore. I would take a few days off and it would feel better, and then I’d overdo it again with photography and driving. I stupidly continued this pattern from until about 3 weeks ago. I went back to physical therapy recently. The therapist confirmed that I have biceps tendinosis and also said my shoulder blade doesn’t move exactly correctly. (He called it dyskinesis.)
I’ve read conflicting ideas. I don’t understand if the mild/moderate pain means I’m damaging the tendon more and I need more rest or if I need to keep doing the exercises because they’ll help me heal. I can tolerate the pain if it’s not something to worry about. Ever since the overuse issue from Aug to mid Oct, I’ve never really shut down the arm and given it extended rest. Part of me wants to do that and just completely rest it for several weeks. However, that’s what I did last year and I ended up with frozen shoulder. I appreciate any advice you can offer.