Baby falls asleep while eating

Hey, just wondering if anyone has any recommendations on how to keep a baby awake while eating long enough to get full. My 3 week old son has been falling asleep faster the last handful of days. I try things to keep him awake to breastfeed but it doesn't work. Then he wakes up and is hungry all over again. I feel like I've been feeding him almost constantly. Any ideas you have would be appreciated!