My body doesn't like running

So, the knot in my shoulder wasn't going away and was getting so painful that I was having trouble breathing. So I went to see my doctor this afternoon. He tested to make sure it was just muscular, and then told me to put my arm in a sling for 3 days (and no running for those three days). He said he could actually see the swollen muscle along the top of my shoulder. Yippee. The good news is that I will only miss track, the bad news is that this means I haven't been to a track workout since August! I should be able to run on Saturday though. If it isn't my foot, its my shoulder. Still all on my left side. Bah.