Could Headache Be Due To Dehydration?

I have had flu like symptoms since last Wednesday with body aches, chills, headaches, severe stomach cramps. Saturday symptoms turned 2 severe diarrhea and headaches. I have had severe headache most of day, taking aspirin/Tylenol without trying 2 upset stomach....HOW MUCH LONGER IS THIS GOIN 2 LAST B 4 SEEKING MEDICAL TREATMENT? IS SEVERE HEADACHE FROM DEHYDRATION? I have never had headaches quite like this- trying 2 drink fluids 2 stay hydrated.