I have had a headache for 3 days accompanied by an upset stomach and dehydration what should i do or eat that wont immediately come out the wrong sid?

Migraine: Migraines and other severe headache types can often present with nausea and vomiting. If you haven't seen a doc for these you definitely should. You may need some anti-nausea medicine or even IV fluids in severe cases. You need to confirm what type of headache this is so that it can be treated appropriately. This may include imaging (ct scan or mri) to rule-out more serious types of headaches.

Fluids and BRAT Diet: Drink lots of fluids with electrolytes (like gatorade) and try a brat diet (bananas , rice, apple sauce, toast. Get checked out if it continues.

Good suggestions: My colleagues have provided excellent approaches, but if this becomes recurrent and turns out to be chronic migraine, would strongly urge use of preventatives, which a neurologist could help initiate.