Hello, Headache is commonly associated with dehydration (potassium-sodium depletion), low BP, low blood glucoses, stress, tension headache, etc. In females it may occur due to decrease in estrogen levels, PMS syndrome, menopausal headache, etc. Sometimes, it also occurs due to poisoning with carbon monoxide, other toxin, food poisoning, gastroenteritis, etc. You are suggested to stay away from stress (physical or emotional), since you are having diarrhea, take anti diarrheal and stay well hydrated. Take water, juice ORS , soups, etc. Take rest and avoid fried food, spicy junk food. Take oatmeal and light easily digestible food. You can take Acetaminophen, one SOS when there is headache. You have neither mentioned your age or if you are a female. You are suggested to get clinically examined by a GP. Get all investigations done. Get treated at the earliest. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician