Suspected Spinal Stenosis. Medicines.

For last one year, I have this excruciating lower back pain, towards left side. It starts once I am in a standing position or walking for 15-20 minutes. If I keep standing/walking, it keeps getting worse. I get relief only if I sit down or arch my back forward (hands going towards toes). I can notice that it is getting worse. I also feel pain now when there is sudden bump in the road. Also, the period of pain starting after I start standing/walking is getting shorter. I am a Type 2 diabetic. Though I quite strictly regulate my diet (I am a pure vegetarian and a teetotaler), I am not able to exercise regularly, especially due to this back problem. I read online and came to know that this may be spinal stenosis. I'll be grateful if you could guide and help me get rid of this pain without immediately resorting to heavy medicines.