My DS is doing the same thing lately. I called the nurse and she said to try and keep him up straight for 30 minutes after each feeding without moving him around a lot (haha, that hasn't worked great).
My DD is doing that too and when I took her to the ped. we found out it was from acid reflux. We give her Maalox before she eats and then burp her frequently, and give smaller feedings. After feeding she has to stay elevated for 30-60 min. HTH
We took DD to the Dr. for this last week. It came on suddenly and had been two weeks of spitting up. She doesn't seem unhappy AT ALL, so the Dr. said it's probably not reflux. We tried putting 1 tbsp of rice cereal in her bottles to make her BM heavier (per Dr.'s advice), but it didn't work. She still spit up. He said it's probably something developmental.
Re: Constantly spitting up??