Falling asleep at breast-help!

LO is almost 4 weeks old. Had no issues ebf in the first two weeks. When he hit his growth spurt around 3 weeks, he started eating ALL. THE. TIME. Sometimes every hour. Now, he will wait between feedings most of the time. But when he nurses, he falls asleep after about 5-10 min on one side. I know he is not full. I will put him down, and within 5 minutes he will be awake wanting more. I have tried switching breasts frequently, rubbing his head and back to keep him awake while nursing, and changing his diaper to wake him up during feeding. Nothing seems to matter, he will fall asleep usually within 5 minutes.