Not likely a pinched nerve. Those you rarely feel at the site of the nerve only. Those you'd notice shooting pain throughout one side of your entire arm.
More likely it's a tight muscle. I can't very well show good stretches in this app, but search for some via YouTube or something. Make sure to stretch both sides equally, even if the other doesn't hurt.
If you can find a good chiropractor, they may be able to tell you what is causing it. Most likely it is poor posture. Sitting at a desk for long periods of time is the most frequent cause, with the second being using laptops frequently for short periods of time. When using a computer, you want your wrists at elbow-level with nearly-completely horizontal forearms. the centre of your monitor should be slightly above eye-level.
There's also a number of physical disorders that will cause pain in that particular area, but almost all of them would cause pain symmetrically and in more than just one spot.
If you have a chiropractor adjust you, know that shifting your spine will change the way your muscles are pulled. Most likely the pain will not immediately go away long-term, but will rather shift to lower in your back, around the middle of your shoulder blade (if the problem is caused by the computer desk posture I mentioned above). This is actually a sign of improvement, and even if the pain is worse at first it will help in the long-run. What you don't want is for the pain to shift to the top or front of your head. That may happen during the visit, but it should not be that way when the chiropractor is done. If it is, don't go back to that one! Do get stretching exercises from the chiropractor or a physical therapist though. YouTube will help, but there's a few dozen affected muscles and at least 2 stretches per muscle, so getting a custom stretching scheme is important.
Don't go to a chiropractor!!!!! I have been suffering from the same problems and was told not to go to a chiropractor by my doctor also My friend had similar probs went to one ane ended up having a stroke from the adjustment.... the chiropractor actually tore a nerve!!! just be careful
The possible reasons could range from sever migraines to nerve pinching. A bad posture or tightening of muscle could also be a cause. It is best you see a neurologist and get yourself thoroughly examined.