self-help for throwing injury, weak back muscles

I injured my back and shoulder muscles doing some new motions with my right arm, swinging/throwing.

Now the affected shoulder seems to have more range of movement than the other one (although it is not painful and did not pop out of place).

Mainly the muscles on that side of my shoulderblade and back are now weak and slightly sore.

Is this just part of healing from the injury - that the muscles are weaker for a while and can't bear as much load?

I'm still trying to do Pilates and exercise whatever muscles I can exercise without pain.

Just hoping I didn't tear anything. No sudden pain or anything, I feel like the muscles just got stretched or overused (it's not a motion I normally do, it was something new).

What can I do?

-put heat packs on the area?
-ultrasound?
-any strengthening exercises?
-generally promote blood flow? Tweet