Breastfeeding mom! HELP!!!?

I am breastfeeding my 2 month old baby, but he doesnt seem to get full. He will drink 5oz of my breastmilk in a bottle since i ONLY pump But after he is done he'll still cry cause he is hungry and i have to give him 5oz of formula for him to be a happy bby. I only have to give him double bottle if i first give him my milk. Does anyone know why he doesnt seem to get full with my milk. Any suggestions in what i can do?