He won't eat, please help

So we uped the dose of prevacid from 15mg to 22mg. Up to this point my son has been eating very well and thriving in weight. Well he is less fussy now but refuses to nurse for more than a few minutes. We rented a medela scale to see how much he was taking and he isn’t taking more than 2oz every 3 hours. I have a tons of milk. So I said I will pump and see what he will take and sure enough, he only took a couple of ounces and then fell asleep with the bottle in his mouth. Tried to wake him up and he wakes up but refuses to eat. He is very sleepy and sleeps for more than 8 hours at night. Before the med increase, he used to wake up every 3 hours to eat. I would be happy about the sleeping at night except that he doesn’t eat much during the day to make up for the night.

I would rather have a fussy baby but one that is thriving I am so worried and lost again