Most often these are the results of osteoarthritis.
You'll probably be better served to use ICE on your back instead of heat. Heat draws blood to the heated area and causes more swelling & inflammation to the heated area, causing more pain. Ice reduces the swelling & inflammation and thus reduces pain. Use the ice for 20 minutes every 2 hours. Wrap the ice in a towel and place it over light clothing. It really DOES help.
I know you said that it irritates you, but perhaps you weren't using it properly. If it really DOES irritate things, then of course don't use it, but at least give it a try.
Have you had an MRI on your low back? It would be a good idea to have a look at that area too. You might ask him for that and make sure it's with and without contrast material.
I know what you mean about the weather -- I'm a walking barometer myself.
I can pretty much determine the weather before it gets here too. It's quite handy actually.
God bless and please take care. Hugs, Lee