feeding question... ?

so im feeding a 3 day old boy which is goin great but when he eats, hell uck for like 5 or 10 minutes on 1 and go back to sleep and theres no waking him up to keep going... i was told that my milk supply could be great and its making him fool... he has lots of wet and dirty diapers so im not to worried. but my other leaks a lot and gets engorged so i dont know what to do with it. should i pump my other as hes sucking off the other? how does that work and is this normal? thanks