Got a test. test 3 times with fixative over 3 days. Don't take anything that might give you false - like mineral oils, Antibiotics , too much garlic. Eat normal and collect the poo in the container with the fixative. Do it 3 times. It's important to use fixative to kill the bugs so no other bugs can grow and they get freezed so you can get a picture of them.
It's the only way to know if you have protozoan or worms. You cannot know anything by the naked eye as many undigested food or fibers look like worms. So it's better to deal with a parasitologist who can identify the cause.
Bacterias like C.difficile, Campylobacter, E.coli and Salmenella can cause Diahrrea.