Why is my baby fussy?

Brittney
My baby has been really fussy the past few days and I'm not sure why...nothing has changed besides his formula (i bf and give formula) but i did that a week ago and this has only been happening about 3 days. Hes passing gas a lot so I'm wondering if its gas but i dont wanna give him anything if it isn't. I'm just exhausted and need an answer please.