The same thing happened with Orson however he lost 2.5lbs in weight. He was very tired and just would not suck properly because he would fall asleep. But he was tired cause he wasn't getting much milk so it's a big nasty cycle. I would wake him every 1.5 hours but he'd still fall asleep during the feed. I had to do everything i could to keep him awake. Tickling his feet, cold wet face washer on his face, changing nappy, undressing him because the heat can make them sleepy too, changing sides etc. In the end my supply dropped too much and i had to stop when he was 4 months old. Other than the above advice im not sure what else you can try but to keep on going. I know it's really hard and stressful but i really hope you can both get through this.