Gassiness more at night?

Hi all....anyone's LO seem to be way more gassy at night? My 4wk old little guy is strictly formula fed on Similac Pro Advance. We noticed a lot of painful gass after every meal with him so doctor switched us to Sensitive. We're on Similac Pro Sensitive for last week and I'm noticing he is less gassy overall, but way more at night causing him to take forever to put to bed. Gripe water and gas drops do nothing for him. Do you think we should switch formula again? And if so what recommendations do you have?