it could also be from heavy let-down. If your breasts feel very full or are leaking try to manually (not with pump) express just a bit. Ie, if I was too full I would have a steady stream without applying pressure once it dwindle down to a drip without pressure then have lil one latch on for feeding. Usually the first few days I had to do this and then just after the growth spurt during start of baby food. Hope that helps! Congrats!
Try taking him from the breast every few minutes to burp him/her if baby is a good eater he is probably taking in a lot of air ..Also be careful about anything strong you are eating or drinking I knew one mom who loved apple juice and drank a lot ..baby was consistently throwing up. If it continues maybe speak to the pediatrician as projectile vomiting is a sign of pyloric stenosis . Congratulations on the birth of your baby I am sure he will settle into a good feeding pattern soon .