I Have Chronic Back Pain

im suffering from chronic back pain for three years..i visited more than 15 doctors for my back pain..my MRI & Xray reports all are normal..some doctors told me to take physiotherapy,some told that due to take lot of strees im having this pain..i feel only good when I take pain killers & gel..by these I can reduce my pain a little bit..i can't stand,walk or even sit for a long time..as im a medical student max time I have to stay in a stressful condition.. :/ sometimes it makes me feel like i'll die very soon..the pain is unbearable..im just done with it..may be I did something wrong in my life thats why God has given me such kind of punishment -_- I dont wanna live like this anymore