like when i sing my stomach is normal only slightly in of course because im singing and i hope using my diaphragm am I ? and then as i sing more or sing higher or longer my stomach goes in just thinking about it my stomach does it. my stomach also goes in when i talk sometimes too. does anyone know if this isn’t right? i don’t move my shoulders as i sing. i think i just breathe wrong when singing. Help? Pretty please? 
When you inhale your ribcage and intercostal muscles will raise and cause your chest and shoulders to naturally rise. When you inhale, imagine yourself inhaling to blow up a balloon, your belly will naturally protrude out. When you sing, use diaphragm support to push out against your belt (like you are trying to make yourself fat). As you use air during exhalation, your diaphragm and intercostal muscles will naturally lower and your stomach will move in the opposite direction it was before.
In order to practice this, lie on the floor with a book on your belly and practice breathing normally. This is what should happen when you are singing.