I've been wrought with UTIs since I started having sex when I was 16. However, it wasn't until a year ago that I realized it happens after every single time (nearly). My bf and I have been together for a year and a half, and it wasn't until I was with someone consistently could I make the correlation. It usually happens a day or two after we have sex, sometimes only 6 hours later, sometime by Monday morning (I only see my bf on Fridays because of our schedules).