HELP 3 1/2 month old baby reflux - projectile acid

Hi,

I have a 3 1/2 month old baby boy. He weighs 17 lbs and is 22 inches long, so quite developed for his age but not overweight. He drinks about 37 oz formula a day in 7-8 feeds.

He is generally a happy baby, smiling, cooing, playing. He sleeps well at night in his crib. Naps during the day are sometimes good 2 hours sometimes bad 30 minutes.

The problem is he will often spit up curdled milk or clear liquid 1-2 hours after feeding and that is when he becomes fussy, chewing hands, wants to be carried, arches back and crying will escalate until he is fed again... (I check the PH of this spit-up with medical grade PH strips and it is always acidic around PH4-5)

Every evening feeds get closer and closer together which I know could be very normal as he prepares for the longest strech of sleep (starting between 8:30-9:30pm) BUT what worries me is that he will PROJECTILE vomit pure ACID. This happens between 5 and 8 pm, at least once. During this period he is constantly fussy and does the "Neh" sound which I heard means hunger... will not let me delay feeds and will have a bottle every 1- 1.5 hours, which he seems to digest as he would soon after spit out clear liquid. Other than that he never projectile vomits milk after feeding, has only a little spit-up here and there which doesn't seem to bother him. But every time he shoots out clear liquid it is quite a large volume (will splash on his pijama from neck to toes) and is the most acidic... PH3.

After his last bottle of the night (8-9pm) which he takes very calmly he will sleep soundly and deeply until 4-5am. He then takes a full bottle and will be awake for about another half hour cooing happily in his crib before putting himself back to sleep for a few more hours.

I am trying to understand why this is happening to him, it's like around 5pm his stomach goes into overdrive and is producing huge amounts of acid that cannot be contained.

He is drooling a lot, his saliva is always neutral PH, and will suck on his hands whenever his tummy bothers him but refuses pacifiers (I tried 8 different kinds).

I gave him Nat phos 6x from Hylands for 2 days:
first day half tablet after feeds, a full tablet a few times when he seemed more uncomfortable (under 6 tablets total/day)
it seemed to make it worse as he was crying more

next day half tablet every other feed
still seemed to be worse than before, more crying

after taking Nat Phos he has huge burps like I never heard him do
I tried Nat phos 6x myself as I have a history of heartburn and I get so many huge burps also, all day long... and sometimes I get reflux episodes while standing up! which I never did before.

Did I make a huge mistake giving him Nat Phos? Should I stop immediately or slowly? Or does it mean it's working making symptoms worse before healing completely?