Some of the members with Thoracic Outlet Syndrome (TOS) get similar headaches - arm use makes it worse usually too.
TOS can be caused by long term repetitive work injuries and a few other things too. Like whiplash, muscle or bone anomalies, hyper mobility...an extra cervical rib.

What type of work /hobbies do you do?

You might read about trigger points too.

We have a TOS forum here if you want to read more about it - I'll give you the link to the useful sticky thread - it's a good way to learn about it quickly.
http://neurotalk.psychcentral.com/thread84.html