Enfacare to Nutramigen

My son was born 11 weeks premature. He’s now 3 months (3 weeks adjusted). He has been struggling to poop, going days without a BM. Also had bad reflux - spitting up after every feed, choking on spit up in sleep.

Been taking Enfacare mixed to 24 cal (instead of 22). Doctor gave us nutramigen today to try out. His weight gain is trending up and doctor said he may not need the extra calories anymore. After first feed he seems a lot more relaxed than usual and not fussy at all.

Anybody have any experience switching from enfacare to this? If so what was your experience?