Question About Spit-Up?

My 1 month old spits up(This started about a week and a half ago) and sometimes it looks watery and other times it looks curdled. Do you think it's the formula? I make her bottles warm (not hot) and burp her after every 2oz. but she doesn't spit up until a little later (Like about 15 to 30 min). Any Advice? I can't get to the doctor til monday