Hey Holly,
Can't answer your vomiting vs spitting up question. However, I have a question for you about the cradle cap?
Are you sure it's cradle cap? I ask this b/c I took my son (second child) to the doctor's b/c I thought he, too, had cradle cap. The doctor confirmed that this is what it was, and he gave me some things to try. I tried EVERYTHING and his head kept getting worse and worse!!! Two months later, I had him back at the pediatrician and because eczema was identified (he started scratching at his skin and started getting red areas behind the knees, etc...), the doctor changed the diagnosis from cradle cap to eczema! That meant that EVERYTHING I was doing was completely counterproductive: I was drying out his scalp that was already too dry! As a side note, I never suspected eczema b/c neither my husband or I have it. After asking around, I found out that my first cousin's had it.
Once I started treating his scalp for eczema, my son was a new boy in a few days.
I recommend you bring your little guy to the doctor to see what he/she has to say. Also, be wary if eczema runs in your family.
Good luck!
T. :)