You know, if you are getting back pain from everyday tasks like this, chances are that your back muscles are too weak. I had back pain on and off for over 30 years. Finally my doctor ordered an MRI and sent me to a back pain clinic. They had me come in to do supervised exercises twice a week on their machines, specially designed to work on back muscles, for a couple of months. I haven't had back pain since! And that was at least 5 years ago!
I let my back pain go on for too many years. My only regret is that I didn't insist on help for it years earlier. I still believe the only reason I got the MRI and referral this last time was because I broke down and cried in front of the doctor because I was so frustrated from the pain and not being able to do routine tasks.
Incidentally, the back pain clinic told me never to apply heat to an aching back. They said the pain comes from inflammation, and heat makes the inflammation worse. They recommended cold packs to reduce inflammation. They also said not to stop moving; if necessary, strap on cold packs in order to keep moving around. I even used a cold pack in the clinic so I could do the exercises longer. Here's a link to the type of cold pack I found the most useful:
http://www.icewraps.net/pro-ice-mult...-back-ice.html
This isn't exactly the pack I got, but is similar. Basically you want a removeable pack that can be placed in the freezer and strong velcro to keep the pack in place while you move around.