7 week old started crying after feeding

My 7 week old is putting on weight like a champ and has always fed great, the last couple of days she is fine with her first morning feed (after she has usually slept for around 8-10 hours) and happily takes her 6oz then the 3 feeds after this (she only eats 4 bottles a day) she has been crying after, so the first time it happened I made her more and she fell asleep content after another ounce but now I am making her 7oz and she is still getting upset, what do you think it is?? We feed on demand

Thanks for reading sorry wanted to get details in 🙈