I just got back from my second physiotherapy appointment. I'm in less pain that last time, probably because I haven't been at work all day. Laura the physio thinks it was so bad last week because my arm was already aggravated from general use at work.
Anyway, she did some more tests, studied my posture and decided that it's probably my radial nerve which is causing the problem. As you can see in my scientific diagram, the radial nerve affects the whole arm. Super. She also noted that I carry a lot of tension in my shoulders and neck, and set me up with a heat pack for ten minutes, which was amazing. I need of those for at home.
She gave me a few stretches to do and packed me off. Back next Monday. I think a big step forward in combating my problems would be having a desk. I mean, I do have a desk, but there's a fish tank on it. I think if I didn't do all my writing sitting on my bed or the sofa, my back would probably be less stiff and there'd be less tension all over. I'm not sure if there's room for another desk in my bedroom though, and definitely not room in the living room. This needs careful consideration.