Since you are a hairdresser and with the arm & shoulder problems I'll suggest you read on our Thoracic outlet syndrome forum (TOS) for short.
It is similar to an entrapment - often a impingement or compression of nerves or even blood flow to the arms at times. Repetitive work and/or holding arms out/up are a common factor.
Does your neck get tight feeling also?

Here's the TOS useful sticky thread for you-
http://neurotalk.psychcentral.com/thread84.html