Not sure if my baby is getting enough milk. Maybe using me as a pacifier?

I had some problems in the beginning with feeding, but now my baby does latch on. I feel the suction and it looks as is if he's swallowing. After about 15-20 mins he will fall asleep at the nipple. I would put him to bed and 5 mins later he'll start crying--sucking his hands like crazy. I'll putt him back on the and this will continue for about 3-4 times. After that I'll give him 2 oz of formula and he gulps it down. I can tell he is hungry because I hear his poor little tummy growl. I've tried all day to feed but it usually ends after many trys and me giving him a bottle....he acts so hungry when i finally give him a bottle. Is it possible to suck like a pacifier and not get any milk??