My 2 months 1/2 old cries during feeding?

My 2 1/2 months old just recently started to cry during feedings. He went from 4 ounces every 3 hours to 2 ounces every 3 hours now. I'm scared because he's not eating enought. I have to pull out the bottle than put it back in his mouthand then he'll stop crying but the next second he will cry again. It couldnt be teething, I think he's still too young right?? Could it be gas? I knowhe does cry when he gas during feeding, but it's not like he's gasing the whole time. I dont know what to do??