Back Support

I am about 100 pounds overweight, trying to lose weight by walking.
However, it causes significant pain in my lower back to walk (even a mile or two).
I tried my maternity belt that I used during pregnancy, which worked great.
Would an obesity belt work, and if so, where would I get a prescription? My doctor is on board with my weight loss plan. Or should I see a chripractor?
I already know that the back pain is caused by my very large stomach (c-section caused loss of muscle tone, sagging stomach fat).