Short term answer is get a unity tactical clutch. I can’t carry in any position without back pain and I can carry all day with the clutch. There’s a vertx brand now that’s half the price.
Long term see a doc and a good physical therapist. Look up “smashwerx” on YouTube. If you’re right stretching is likely not the answer. There are alignment issues. Carrying a gun takes a toll on the body. You’re body is telling you something isn’t right, listen to it. But resting is not the answer. If a doc tells you to just take two weeks off, beware.