I've had three surgeries for rotator; two times on one side and once on other. Not fun.
Absolutely do not go heavier. YOur body is trying to tell you something. If you can find a physical therapist that has been around a while (say 15 years at least) that would probably be a good option. The younger ones I saw did not have the experience, and one of them actually had me doing exercises that made it worse. The guy I found was an archer and very good. He was very helpful.
If he's an experienced PT, he will know if you need to see a doc. If so, will probably be an orthopedic. My bow arm ached badly the last go round. My PT told me it was probably ligament damage where the rotator and bicept tie in. I fought it for several years and finally had the surgery. My PT was right. My tear was medium, but my ligament was shot.
Good news it that is can be fixed, and hopefully yours is a simple matter of some well chosen exercises. Take care of it now though, or it will likely get worse. At least mine did.
Good luck.