Vomit every 20-30 minutes... Dark earlier, now clear

Watery diarrhea

How long has this been going on? What is the age of the person this is happening to? Any pain, fever, or other symptoms? Dehydration is always a concern with frequent vomiting and diarrhea. Could try small, frequent sips of water, but if it continues, it would be wise to see your doctor to determine if it is perhaps just a stomach infection, that has to run its course, or something else causing it. Depending on the cause, they may give medication to help with the vomiting.