When I first started carrying, it was a g23 in an iwb behind my left hip.
Wallet was in the left rear pocket.
Started to get sciatic pains in the left side of my back.
Did the doctor visit, basically told me to stop carrying that way, and MOVE MY WALLET!
This was my first foray into aiwb, and it was very strange at first, but the pain left almost immediately.
Chose a smaller kydex wallet that I now carry in my front pocket, and got a better belt, [mastermind tactics] and have not had a pain since.
FYI,
57 years old, 5'8", about 190.
Hope this information is helpful somehow.