When I've done my back it's luckily always gone by just resting but also keeping it moving as much as you can with gentle stretches and stuff. If it lasts more than a day then I'd consider the doctor. Also, eat your avatar regularly....
Most gyms / sunbed shops / etc will be able to do massages (without extras
) or check the yellow pages. I find with some massages, coz I'm quite a big bloke, the masseuse can't do it hard enough, so considering asking for a bloke next time I get one...