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Chronic diarrhea can be due to parasitic infestations, hence a stool test is a must. Other causes are irritable bowel syndrome, celiac disease, crohn’s disease, malabsorption syndromes, pancreatic diseases, diabetes, hyperthyroidism etc. HIV too could be a cause, though chances are less after a single unprotected oral sex. Yes, it can also be a fungal infection. It is difficult to comment beyond this without examining. A comprehensive investigation is required keeping all the points in mind. Please consult your PCP to start with.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!