left arm pain. pulled muscle? or blood clot??

[Vedabug54]

So two weeks ago I was walking up the strairs with my son in my arm and a bag and my arm just got extremely painful. Like I pulled something. And its been hurting off and on ever since. It got better than I took my son swimming and it started hurting again. I went to the doctors and he said it was a pulled muscle. Did an xray. Sent me on my way. It went away for a few days and the pain is back. It moves from the outside and insinde and in my shoulider. The worst pain is in the inside. Should I be concerned? I'm terrified its a blood clot. But I figure if it was a clot, it would have moved or my arm would be swollen. I don't take birth control but do smoke. Should I be worried? How long should a pulled muscle last?

[Vedabug54]

Any help?