It could be just severe IBS. Were you unusually stressed before this happened? Have you eaten something that could be upsetting you - something new perhaps?
On the other hand, could it be an infection, maybe giardiasis? Giardia infestation is more common than you may think.
I think you should see your doctor but in the meantime maybe take some Pepto-Bismol. It always helps me and is pretty harmless. Just be aware that it will cause your tongue and your feces to turn black temporarily. Brushing your teeth straight afterwards helps prevent your tongue getting discoloured.
~~~I learn by going where I have to go~~~