Could be dysentery.
Did you have food from outside like restaurant or any parties?.
Next Steps
start on Metronidazole 400 mg thrice daily for 3 days. ( avoid this medication of you have consumer any alcohol or any softdrink containing alcohol as I might lead to adverse reactions)
Have plenty of Water, it possible ORS or ELECTRAL
Health Tips
visit a physician near by of problem persist even after 24 hrs.