It should be that you are too pursuing weight, and your chest muscles should not be too heavy. If you exert yourself, you will lose your shape, and your body will borrow muscle strength from other parts. According to your situation, it should be that your waist and lower abdominal muscles are overexertion, or it may be the so-called pc muscle (the muscle that controls urination).

It's okay. After more than a week, I got used to it, just like when you just practiced your muscles, but I still suggest that you don't blindly pursue weight, ensure the regularity of your movements, and try not to use other parts to exert strength.