I have a newborn who is throwing up a lot. How much is too much? When should I consider going to hospital? She is a female and is three weeks old

You . You should contact you pediatrician as soon as possible, first to make sure she is not dehydrated and second to make sure she does not have a GI problem that needs addressing. This may only be a case of "spitting up" after a feeding but it requires immediate evaluation by her physician.