I have been doing push ups daily for exercise and strength, usually I do them by myself in my room so I can exercise shirtless, I did one in the lounge and my brother noticed that my back really curves. He did some and his back doesn't curve.
In detail: My back arches up and then down really steeply to my ass. I can't stop it from happening to matter what I do, I have spent a lot of time doing press ups in the mirror to try to fix it, nothing has worked. When I go on all fours it goes away but when I do push ups or planking it comes back, and it looks disgusting, one big stupid curve.