Men often carry their wallets in their back pockets. While this is no problem when you are standing or walking around, when you sit down it is like sitting on an uneven step, and if you are diving or sitting for hours it is a recipe for lower back discomfort.
I once had a truck driver who came to me for relief from his chronic lower back pain. When taking his history I discovered he had driven with his wallet in his back pocket for 35 years and on x-raying his back, his entire spine had shifted and twisted to accommodate this – you could even hold up his wallet in the space it had created under his right hip and it fit perfectly!
So - if you must carry your wallet in your back pocket, take it out when you sit down. Or better yet, put in your front pocket instead.