Baby pooping..please help

My baby has been having poop explosions... He's three weeks and it's starting to concern me his stomach as he's just hanging out I can hear his stomach making bubbling noises like crazy and is super airy. I'm trying to determine what's causing his stomach to be this way and trying to determine if his poop is diaherrea? Couple things... I did eat cauliflower the last few days and didn't realize that can cause gas... Also I'm on safe prescribed anti biotics due to my infection from c section. So I stopped as of today giving him my breast milk as I'm worried that could be a cause? Or can it be the formula I'm giving him? He's been drinking it since two weeks ago when needed to supplement.  However didn't poop like he's been the last couple days.