My son was only on formula for a short while. I had hoped to go straight from breast feeding to whole milk but nothing I could do at 7 months could persuade him to stop biting me.
I cannot remember which formula I tried out on him first, but then I noticed that the store (Meijers) had a store brand, that was made by (I think) Wyeth Labs. Everything was comparable with nutrients, etc but the store brand was anywhere from $1 to $4 cheaper than the name brands. Being the practical child of a tightfisted mommy, he never had any problems with it and I switched him over to whole milk ( per pediatrician) at 10 months.
If John is having problems keeping regular formula down, you may want to try soy ( of course, after talking to the doctor, ad nauseum disclaimer) or perhaps a dose of the greatest elixer of infanthood:mylicon drops before a couple of feedings to see if maybe that might help.
If you are switching back and forth between Brand A and Brand B and one may be a low iron formula the other a regular iron formula (as an example) you could be giving him, to put it in a better vernacular, engine knock
( gassiness and fussiness.)
My dipshit dimwitted sister in law was doing breastmilk once or twice a day and two different kinds of formula ( one was at her mom’s -the sitter-house and the other was at her house)for the rest of the feedings and could not figure out why the baby was crabby and gassy all the time. Of course the Doctor, busy with real problems, diagnoses colic and this puts my DSDW sister in law in “My baby has colic so pity me” mode. ( Not in this life, girly) Dr. Shirley comes along and sees what tomfoolery is going on and sets them straight ( in my usual callous fashion of “The kids got engine knock, you’re mixing high octane with ethanol and gasahol.”)
Good luck and condolences on the clothing