Hi thanks for asking question.
First you could have simple
gastroenteritis like infection.It can lead diarrhea.
Take
ofloxacin and
ornidazole combination drug for few days to cover bacterial infection.
It could be by taking outside food and infection following that.
Here you might have
stomach flu .by viral infection .so can lead headache as constitutional symptom.
Drink more water with ORS.Because
dehydration can precipitate headache.
Avoid smoking .
Avoid fatty and fried food for few days.
Take spicy food very low.
Small meal at frequent interval taken.
Take rest.
Probiotics can be taken to replenish bacterial flora.
Get your stool examined it can reveal parasitic egg or trophozoites which is treated accordingly.
If your symptoms worsen then USG done.
If needed endoscopy also useful.
Wish you good health.
Dr.Parth goswami