Wtf have I done to my arm

[MintyGreenDream]

It's been really painful for over a month if I move it away from or towards my body.Its the bicep and tricep? Area.
The thing is I haven't actually knowingly done anything to it.It definitely feels muscular.Any tips to help it go away
?

Trapped nerve. Physio needed.

If you hold your arm up at shoulder level and move it left to right does it hurt ?

@Kangaroo not particularly.It feels like it would if it had been whacked or I'd fell on it