What Causes Recurring Tingling Sensation And Pain In Right Arm?

Hi, for the past six months I've noticed a strange tingling that occurs on and off in my right arm, it has also been 'heavy' and achy. This doesn't happen all the time but is getting more frequent. I've now noticed a lump under my skin on the upper part of my arm, it's became noticeable because I've lost a large amount of weight recently. It is completely painless.