Pain in left arm after I slipped over and fell

About 6 weeks ago I slipped over and fell on my left side hurting my left arm. Consequencely I was taken to Hospital to checked by a Doctor for any likely fractures. I was told that there were not any fractures and was told to take painkillers indefinitely. But nevertheless I am now still experiencing occasional pain. For an example, whenever I stretch out to reach for something or to try to scratch my back with my left hand, I experience quite a severe pain in my left arm, which lasts approx 15 secs. This problem does not occur all of the time.I have approached my GP explaining to him the problem. He has prescribed me Ibuprofen 400mg tablets to be taken for 2-3 weeks. Somehow, I have my doubts whether this medication will be a remedy. My personal belief is that the problem is a nerve disorder which is likely to be causing the pain. Can a Doctor please advise me on this matter. Thank you