Are you breastfeeding? Or formula? It could be a lot of different things...He could be sick or it could be that he isnt tolerating the formula well. Its normal that if he is throwing up, hes gonna want to eat again so soon! I say use your "mommy instincts"! It wouldnt hurt just to call the nurse on call at your doctor/his doctor and ask. She may be able to tell you more! Good luck hun!
Lauren

I would take him to the doctor if I were you...Has he lost weight? Maybe they can prescribe something for him to help him keep his food down. You dont want him to get sickly and weak. He needs his nourishment...

Mackenzie is the same way and we put her on alimentum stuff and the doc told us to put rice cereal in her formula so that its thicker and may settle better. Ask ur doctor when u go in. Are u breatfeeding?