Kidney infection can also produce back pains, but I'm not sure if it's really in the lower back, or a little higher. (But don't freak out, OK? ^^)

Yeah, a bladder infection will cause back pain. But its not that serious most of the time it will clear up all on its own... and a heating pad WILL help... heat is one of the ways the body fights an infection (fevers) and like I said grapefruit juice.

From the sounds of it your body is already winning this battle.

Could be a lot of things, but back spasms can come on for no particular reason. I get them once in awhile. A few weeks ago I bent over to pick up my lunch box and my spazzed and I ended up on my knees and barely managed to get up off the floor. Rest, Ibuprofen and heat, it got better in a few days.

Walking backwards does help to loosen up the lower back. For ice packs, plain ole cheap white corn syrup, in ziplock bags and frozen are great. You can make any size you need, they're cold, but stay pliable. Just remember to double bag, don't want that sticky stuff loose in the freezer.

I would get to the doctor to rule out any major issues. Hope you feel better soon.

I get lower back pain when I don't exercise. I sometimes get it when I do exercise. In the long run, consistent exercise has reduced the frequency, duration, and intensity of painful episodes. I am so much better than I used to be. Getting the weight off probably helped, too.

My exercise includes stretching, especially hamstrings. This yoga DVD helped me a lot: http://www.amazon.com/Yoga-Stress-Re...f=pd_sim_mov_4