I Have Had Pain For A Month In My Right

I have had pain for a month in my right upper arm on the dorsal, slightly medial side. MY arm hurts primarily when I stretch my arm to the side at shoulder height, but sometimes when Inturn my car's steering wheel. The pain is exactly as it was when I first felt it. Can you suggest what it might be and whether my internist or orthopedist should be consulted--or whether I might try some sort of home remedy first? I don't know what led to this condition. I'm very active. Thank you!