@mew I'd show you the 'secret damaged artist handshake', but, well, you know. *holds up hand in a wrist splint* XD
That might be a direction to look, you might have some extra forces compressing the thoracic outlet areas. In which case, maybe some gentle stretching of your back and chest/shoulders before arting may help. Worth a try, perhaps - gentle being key. Just to loosen things up to start.