Please help. Has this happened with your baby’s

I had my baby June 1st at 36 weeks 4 days. I had an 8cm cyst/tumor on my ovary that the doctor wanted to remove so she didn’t want to wait any longer. I came home 2 days later but My son stayed another week because his oxygen kept dropping when eating and wasn’t eating enough and kept loosing weight everyday. Finally after a week he stArted to eat more and gained a little weight and his oxygen wasn’t dropping anymore. He’s been home for 3 days he had been eating good 40-55 ml every 3 hours and they want him to eat 45ml and since yesterday he has been eating 20-25ml and then 3 hours later eats 50-60ml and then 3 hours later only 20-25ml Again. I can’t get him to eat more I wake him up change his diaper and he still doesn’t want to eat more. I’m really worried he will start loosing weight again and not eating enough. Has this happened to any one? 😞