That’s so scary, I hope he feels better soon. My dd’s MSPI horrible rash improved after about 10 days but it took almost 3 weeks for the vomiting and stomach pains/heartburn pain to subside. She was also on a high dose of losec though, so it was probably a combination of the 2 things working well together at the same time. Could you ask your doc for something to calm the stomach acid? A ppi?
I found that every day just seemed to be a little better for my dd after 10 days on the formula or so, not a huge change happened overnight but maybe 15 minutes less crying one day and one less vomiting spell the next and it went that way until one day I realized “Hey, she hasn’t puked yet…and it’s 6pm!!!” After that point she did great.
Good luck to you