sorry to treat you like an idiot - i know you've shot dope before so i could be way off --- but i've gotten this before, and unless i've totally misdiagnosed my own problems, i always just figured they were bad misses - for me, it'd be swollen as fuuuuck for maybe a day and then slowly go down over a few days, how long's it been now? for me i think it tended to happen when using blunt rigs and maybe getting a vein but then going thru it and pumping a bunch of uppers out the other side. other than temporary discomfort it never caused me any problems - but it's been a while since it happened, 6 months at least.
EDIT: and just gunna second the opinion - don't go for the wrist. it's a real, real tricky spot.