J.A.
I have had the same problem with my 4 1/2 month old daughter. She was spitting up a lot and also went a few days without bowel movements. I started seeing black spots in her stool. My Dr. tested her diaper and found traces of blood, and he feels that she is allergic to dairy in my breast milk. I have cut out all dairy products (which is not easy!) and have noticed a big improvement. Not sure if this is what is happening with your little one, but it might be worth talking to your pediatrician. Good luck!