Formula question

TheFutureMrs.O

I am an EP. I make a great amount of milk. Baby drinks a great amout of milk. 31 oz a day. However, baby is not gaining weight all that great for some reason. He is 13.2 pds and 5 months. He has dropped in his curve to like 3rd %tile. We went to Dr. On Friday for a follow up on his ear infection. I expressed my weight concerns. She has recommended us to add Formula to my BM to up his calories to try to beef him up a little bit. I am totally OK with this. We started right away Friday evening.
Here's my question. How long do you give it before you decide a certain brand formula isn't quite fitting for your baby? He's been pooping more often since we added the formula and I'm afraid he's not even having enough time to take in the added calories or nutrients. Just wondering when we try another brand. 3 days? 5 days? TIA.

Maelara

I think 2 weeks but I'd give it a week and if you feel it's not the right fit, switch it up. Just make sure to mix the old and new formula for a bit so it doesn't hurt his tummy.

ASmallWonder

It's close to two weeks before their systems adjust.  More pooping is normal because they can't use every bit of formula the same way they can with BM.  As long as it's not literal diarrhea, don't let that be much of a concern.