I pulled a muscle directly under my shoulder blade (dorsal muscles?) a couple of months ago while carrying something heavy - not as I picked it up but as I was walking with it, I felt the muscle "go". It recovered well but since then about once a week that muscle will spontaneously start to hurt, as if it has been pulled again. Often, I'm not doing anything at the time, I can just be sitting there and suddenly it "goes" again. When it is not sore, I can exercise just fine (pull-ups, press ups, etc, not heavy weights) and this doesn't seem to trigger it.
Often, the pain will suddenly stop just as suddenly, rather than gradually fade.
I assume I've hurt the muscle in the original pull but should I do anything about it? Or is it just taking a long time to heal?