10 month old throwing up.

my son has been throwing up since friday. it was at night in the middle of the night at first. now he's thrown up twice yesterday and four times today. took him to the doctor and they didn't seem worried about it. i just don't understand why he'd be throwing up so much. he acts fine the rest of the time that he isn't throwing up. he's throwing up bottles and food. he had been prescribed ondansetron by urgent care awhile back, but his pedi suggested i not give that to him. any thoughts or suggestions?