Frothy vomit..

LJ • 1 baby girl with another baby on the way
Gross title I know.
​The last few days when I have been sick it's been frothy saliva type liquid. It's not a huge amount but it's gross.
​In the mornings this is sometimes yellow.
​What is this??? 
​I have been eating regularly but for some reason the food doesn't come up.
​Have an appointment with my consultant next week and will mention it to them then if it continues. Just wondering who else has experienced this?