Need help!

Okay so my baby is a week old and I have took home the ready to feed bottles from the hospital finished those off n switched to the powdered formula both are the blue similac advance ever since switching he has been spitting up a lot more n seems uncomfortable he is still having the same amount of pee n poop just spits up a lot more then he did with ready feed so I went n bought some ready feed  and just switched throughout the day he is only spitting up after the feeding of the powdered what can I do is it just because I just barely started him on it should I wait it out another week or two or should I just go strictly ready feed ???? Please help thanks