Almost 4 month old

Cece

My little one is almost 4 months old. He was eating like a champ and now it seems hard to feed him. He will eat a little then get fussy so then i let him play then drink again later. Anyone else? Also, for those that breastfeed, how do you stop your baby from biting (no teeth yet) and pulling your nipple? How do you get your supply up? Mine dipped suddenly :(