Get a vag infection 7-10 days after sex every time. All bad stuff ruled out. Metro and diflucan (fluconazole) again. What's going on?

Bacterial vaginosis. Need more info to be definitive, but one possibility is that if you only have a single male sexual partner they have the bacteria that infect you colonizing the skin of their penis and then recolonizing your vagina with the same bugs you have just eliminated with medication. Discuss with your doctor.