Please help my black moor goldfish!?

You tank is way too small, need a minimal of 30ish gallons. they get HUGE! he is probably sucking on rocks to suck up any food or nutrients, etc. my goldfish do it all the time. your fish is sucking air at the top because he needs more oxygen in the tank and he if he is just doing a "waddle" that's how fancy goldfish normally swim.