Oh man, muscle tension seems to be my specialty. (Not in a good way!) I've probably always held tension in my neck & shoulders when stressed, which definitely causes headaches. In fact, after doing really well for a while, yesterday my neck & shoulders started tensing up. For me, this causes headaches, back tension & tingling in my right arm. Even if insurance doesn't cover it, I highly recommend seeing a massage therapist if this is a persistent issue. In my area, an hour massage is under $100 (& you can opt for a 30 minute session if money is really tight). I have a friend who is a massage therapist & after putting it off for months, I finally did not one, but two, sessions with her. The massage helped a lot, but the info she gave me about various muscles & where to work on them was an amazing help.
But realistically, since I can't get a massage every time I tense up, I started researching stretches & exercises I can do at home. I started doing these a few weeks ago to help with the neck & shoulder tension: http://www.mindfulwellnessmassageandbodywork.com/media/Neck,%20Shoulders%20&%20Arms%20Stretches%20001.jpg
They are quick, easy to do & really help you loosen up. I do them first thing in the morning now every day before I start my other exercises (I started a routine to help with my anxiety & muscle tension because I'm a mess.). I do them again during the day if I feel tense.
And if you can get your girlfriend to do more massage for you, try having her work on your shoulder blade (almost underneath it). There's a connection between there & your neck. (If you can reach it well enough on your own, you can do it -- it's just easier & more relaxing to have someone else work on it!) And gently massaging your armpit area might help your shoulders. Seriously, try it! Good luck -- I know how awful it feels...