Back Pain While Running. Out for this.

I had the lower back pain problem back then during school days but with proper medication and using the back belt it has somehow got reduced but not completely. I started gym but unfortunately couldn't continue due to the pain and because of which i gained lot of weight as my office job is a sitting job. To ensure i reduced i started jogging. For few days i ran for 10 min and couldn't see any pain but in the later stage when i completed 15 min my entire lower back from right to left started paining(Especially on the right side i can feel like i am getting a cramp) as if there is lot of weight put on my back (Once i bend down i will be reduced). I want to jog for more time to build stamina and to be healthy. I can't invest more on therapy and other costly treatment. Please suggest me a way out for this. Thanks. Appreciate for some good leads of Doctor as well.