Possible tummy problems from Prevacid

My daughter has been on Alimentum (RTF for 2 days, canned the rest) for
a week now and she is not tolerating it very well. She can’t sleep and
wakes up spitting up. And her burps are very violent. The worst is when
she wakes up in the morning screaming from needing to poo. That has
been her problem from the start. She has always been very gassy and
after trying Goodstart Supreme and then Soy she stopped pooping all
together. So the dr put her on Alimentum thinking she had an
intolerance. Now I hear that it could possibly be the Prevacid she is
on (she is 9lbs 4oz and on 3/4 of a 15mg tablet once a day) that has
been causing all her tummy problems and not the formulas. I am so
confused and don’t know what to do. I have seen 3 different drs in my
office and all have been sending me in different directions. I have
been told that the ready to feed is better on them but I can’t afford
that. I can hardly afford the canned. Any advice?