Dear Marie Gray, based on your history looks like you may be suffering from some heart related condition. So would like you to rule that out first, as early as possible. For that you would have to get your Electrocardiogram taken and may be a stress test too. Another cause for the pain could be, muskulo-skeletal related (muscle, tendon, bone, etc), which is a non urgent cause. I hope you have not sustained any trauma to your arm recently, which could also be a cause. To relive yourself from this pain, in either case, I suggest you give your arm, some rest, avoid lifting heavy objects. A warm water bag massage would also relieve pain in case. For pain you could take an analgesic tablet thrice day, after for for probably 3 to 5 days, till you feel better. A locally applied balm/analgesic gives temporary relief too. Sometimes muscle cramps also give rise to such pain, to prevent this you need to drink plenty of water (minimum 2 liters / 8 glasses) and especially fluid and food containing electrolytes like, lime water, coconut water, citrus fruits, banana, etc. I hope I could answer your question. I wish you good health.