Hello,
Headache might be due to dehydration secondary to diarrhea.
If this diarrhea is recurring, Irritable Bowel Syndrome has to be ruled out.
If associated with fever or other symptoms cold/cough-viral gastroenteritis to be ruled out.
If headache is associated with nausea/ vomiting or blurring of vision, there might be other pathologies causing tension in the brain.
Next Steps
Stay well hydrated-rehydration therapy.
If symptoms doesn’t subside or progessing-consultation to be done.