The correct Diagnosis for pain in my right arm...

For a few months now i have been having pain in my right arm, running below and parrallel to my bicep . I have been unable to find a diagnosis on the net but i’m assuming it’s a muscular problem, maybe a tear?. If i stretch a little bit there is pain, if i touch the area it is strangely numb, if i press firmly against the area it is excrutiating. What is wrong with my arm i wonder?? I’m only 31 and this is the tip of problems i have with my body lol. I have had lower back problems over the last couple of years but i don’t think it is linked to this. Hope you can help?