If you don't want to go to the doc right away I'd start w/a deep tissue massage and rest it for a couple weeks.
Also, if you can find someone that does Active Release Therapy, I'd try that too.http://www.getbig.com/boards/index.php?topic=267611.0
I ended up having a massage therapist who "sort of" knows ART do it to my shoulder and it really, really helped.... It was bad again recently because I spent 4 days in bed but had a massage yesterday focusing there almost the whole time and feel sooo much better.
Hope you feel better soon.