I'm Not Sure What I Did Wrong

Hi,
I am a full-time nanny for a three month old little boy who has acid reflux. I've done everything I was supposed to with him as far as feeding, holding him up for 30 minute after he eats, not laying him on his back for long periods of time, and using a wedge while he sleeps. This little boy screams ALL DAY LONG. I walk with him, rock him, hug him, try to distract him, pretty much anything to make him happy. At first I thought it was because he was in pain but I've noticed that its when he gets angry. He gets angry when you don't hold the bottle a certain way and when you dont let him push down on your stomach with his feet. He's just a very angry baby. I've tried everything I can think of, talked to the parents and all they say is well hes a baby. I know for a fact that the mother holds him all the time and never puts him down, so I'm not sure if hes spoiled. I thought three months was to young to become spoiled. So one of my questions is, is what do I do with this baby? Does anyone have any suggestions on how to calm him down? The mother does not want him crying, she gets very upset. Since he has acid reflux she does not want me leaving him alone at all, as in like going downstairs to grab something to drink while he sleeps really fast. He sleeps a lot, probably 4 hours out of 7. She also gets angry that hes always asleep. Today when she came home, she got really angry with me because he had slept a lot today. She has told me I can't eat upstairs, which I'm fine with. But when this baby is awake all he does is scream constantly. The only time I really have to eat is when he's sleeping. She was VERY hateful and rude today when she came home. So my 2nd question is, how do I handle this? What can I say to her so she knows I'm honestly trying my hardest? Thank you so much for helping me!