18; 118 pounds, 4 months experience. Already experiencing lower back issues.

Cars have always been my passion, I started working full time 50-60 hours a week 4 days out of high school. I have experienced lower back pain before but only when I have to work on my lower car at home, constantly bending over. Recently it has got a lot more severe, can’t run without pain, can’t twist without pain. The shop I work in requires us to remove all wheels off of every vehicle that comes into the shop to complete an inspection, this entails truck wheels that weigh up to 80 pounds. What should I do to fix my lower back pain. Go to the gym and train to gain weight and muscle. Or is this a career ending problem, as it might worsen in the future? Will I have to go school now to find a job I have 0 passion in? What is the longevity of mechanics body, I want to be able to play with my kids at 50 and still be able to snowboard. How should I go about this.