I've been having diarrhea for 10 days without any stomachache or such thing. i tried different foods but it didn't make any change. what's the problem?

Diarrhea : Diarrhea for 10 days often starts as an infection. Two common reasons are viral and food-related infections. After infectious diarrhea often people can not digest foods, like dairy, for some time due to the temporary changes in the intestines from the microbial. I suggest speaking to your doctor about it and avoiding dairy and heavy foods for one month. You may benefit from stool testing

Acute diarrhea : Common causes are intestinal Protozoa: Giardiasis, amebiasis, cryptosporidium. Parasites: cyclospora, Isospora and microsporidium. Other causes are post infectious irritable bowel syndrome and small bowel overgrowth syndrome. Keep yourself well hydrated and see a doctor for diagnosis and treatment. Hopefully it helps.