Why won´t my doctor prescribe s stronger pain medication?

No easy answer. It is difficult to say why your doctor won't prescribe a stronger pain medication without knowing the details of your specific clinical situation. However, rarely is pain medication the answer as these are only pain "maskers", whereas we want to look for the source of the pain and treat the cause of the pain. Discuss this with your doctor.
Pain medicine. I am sure he prescribed what he felt was best for you based on your history, his examination and also on evaluation of tests and an assessment of certain risk factors. I think you should see him again and discuss or get a referral to a pain specialist - remember just because you have pain does not mean automatic pain medication.