I Have A 6 Week Old Infant Son On Gerber

I have a 6 week old infant son on Gerber formula after changing from Similac due to gas & fussiness. He still screams like he is in pain sometimes while he is feeding,sometimes when he wakes up in his sleep, screams as his whole body turns red. He is gaining weight really well, no spitting up or vomiting.What else could be the problem? Using Mylicon drops which seems to help sometimes