Have you talked frankly with your doctor about your concern? If not, I urge you to do so as soon as possible and if he or she doesn't seem to take your concern seriously, seek advice from a doctor who will. I'm not a doctor, of course, but from time to time I get letters from people who have become addicted to painkillers in this way, and it's a very serious matter.
Let me assure you, however, that God knows your situation, and there's nothing wrong with seeking medical help for your back problem including pain medication if necessary. In fact, we should be thankful for all the advances in medicine that God has given us through gifted researchers. The Bible reminds us that "Every good and perfect gift is from above, coming down from the Father" (James 1:17).
At the same time, I hope you won't become so focused on your physical problems that you ignore your spiritual health. Physical problems tend to overwhelm us but they also should remind us that life is only temporary, and this world is not our final home.
Are you prepared for that day when you will enter eternity and face God? You can be, by turning to Christ and committing your life to Him in faith and trust. When we know Him, we know that nothing "will be able to separate us from the love of God that is in Christ Jesus our Lord" (Romans 8:39).