Bad diarrhea. Could it be from fluconazole side effects or virus?

Perhaps. Diarrhea is a side effect of fluconazole. But, it's possible that the diarrhea is viral. Did the diarrhea start with the fluconazole? Have you had antibiotics prior to the fluconazole? Antibiotics can cause a type of diarrhea in of themselves. If Fluconazole is for a yeast infection, i would recommend taking probiotics to help with this as well. Go see your pcp if not better.