I'm taking painkillers since week for severe back pain, now it seems nothing work for getting pain better, it's in the middle of my back, should i worry?

Pain: If you are taking pain killers and they are not helping it is important that you have a full evaluation by your physician to assure that your diagnosis is correct and to assure that you are taking the right medication. Escalation of the dose of medication is not prudent without the advise of your physician. You may have a severe underlying condition or you may be treating your condition wrong.

Need evaluation: It may not be what you want to hear, but there is no way to guess at this. You need to see your doctor.