Pumping...

My son will be a month old on Tuesday, I've been breastfeeding.. we have my nephews birthday party tomorrow, so I figured I would pump him a bottle. I pumped for 30minutes straight, and didn't even get an ounce.. is this normal? I feel like I should be pumping a lot more..all the articles I read say I should be pumping 2-3ounces. So I'm wondering if I'm feeding him enough.. he's gaining weight, but he eats almost every hour, sometimes even more.. should I switch to formula?? I'm a first time mom, so I'm jot sure what to do.