If your really in pain as in agony, I'd suggest you go and see your GP particularly if its your lower back is killing you- it could be worse and you have a slipped disc. If its only a few muscle spaismw however which is seems most likely in your case the best advice would be to rest and sleep with your lower back supported. Ie elevate your legs on a buusto or pillow or something. And painkillers...thats the best any GP will do. LOL