I need some reassurance

When my baby was born premature at 36 weeks, 6 days, he weighed 4.4 lbs, and measured 17 inches long. Very small baby. When he was discharged from the NICU, we took him to a doctor a few days later. While there, the topic of feeding came up, and my baby’s pediatrician had me giving him (him being the baby) enfamil infant, and some gross smelling liquid iron supplement crap. My baby will eat like a cow if he eats at one of Mom’s two convenient locations, but when we have to supplement for formula, or add in that iron supplement stuff to s bottle of pumped milk... well... he won’t drink the formula very much, and he’ll drink about half of what he normally does with the iron supplement. Not only that but he just can’t seem to keep either down for long. After a while he regurgitates a little bit up. breast milk though, he’ll drink all day, and hold it down real nice.

As a first time parent, I’m very nervous that he’s not getting the nutrition he needs. Doc says everything is fine, and to just let the baby take as much as he wants, or at the very least, increase the amount he drinks, a little at a time. The baby seems to be fine. He’s very active, and very aware. His reactions to light, sounds, and physical stimulation are normal, and consistent. His BMs are also consistent, in all aspects.

Am I doing enough? Am I doing too much? Any tips? Mama is the strong one, I’ll admit to that. She’s confident the baby is perfectly healthy but me... I’m a dad that has more worries than there are people on this planet. I just want to be told I’m doing all the right things. I don’t need to muck up my rainbow baby...