I just got over a very badly pulled trapezius. Some days it hurt so badly I could barely pull on a tee shirt. I was traveling so I wasn't working out or lifting heavy weights regularly, but it managed to linger for TWO MONTHS anyway because I never fully rested it, either. When I got home and finally saw a doctor he told me to apply heat and ice twice a day (15-20 minutes with a heating pad, then 15-20 minutes with a bag of ice) and take 2 Aleve twice a day. Within a week the pain was gone. I'm back to boxing at my gym and starting to lift a little weight. I'm still going slow just in case, and I sometimes apply ice right after a hard workout to preemptively contain any swelling, but it looks good.
So heat, ice, pain reliever, and rest. Just rest your shoulder, though - my doctor said cardio is good for healing and encouraged me to keep running and going to the gym as long as I left my shoulder alone. He said if it wasn't better after two weeks that I should get it looked at again, but thankfully that doesn't seem necessary. I hope your healing goes just as smoothly.