Is it a babies reaction to adjusting to Rice cereal or may he not be able to tolerate it?

My ped told me to put my 1 month old on Rice cereal so i did... the first two feedings he kept down, the 3rd he spit up a good amount, but im wondering if it is because hes adjusting, having a reaction to the Rice Cereal, or because i put him in his swing after his feeding? Dont critisize me im just needing advice, no i am not a lazy mother or bad mother because i put him on it eithr because now he doesnt act like i starve him and he sleeps better. Thanks moms