When will the pain stop?

I now have a new, and vastly more intense pain in my arm, where it meets my shoulder near my armpit... when I lean forwards too far I get a feeling like I'm being stabbed (not that I've ever been stabbed, I'm guessing about that one).

Instead of the steady, deep burning in the rest of my arm, the new pain is sharp, intense and takes my breath away (and also gets me sort of jumping to attention as standing straight is the only way to stop it, though there is a shadow of pain always lingering there!)

I just don't know what to do. I loathe the prospect of going back to our useless doctor, but I don't think I'm going to have much choice if this doesn't ease soon!