Ok so I'm about 7/8 weeks pregnant. A couple days ago I vomited this horrible yellow watery vomit, I didn't think much of it but it happened again today. Could this be normal morning sickness or something more serious? Or could it just be lack of food in my stomach?

The colour of your vomit would be determined by what you've ate/drank in the past hour or two. Lack of anything will force vomiting the stomach acids. Stomach acid is clear, however it is mixed with bile when vomited and usually becomes yellow.