Dr thinks UTI might be chlamydia?

I've had this uti that keeps coming back immediately after I finish my antibiotics. My doctor has told me in situations like this they would consider chlamydia. My only partner my whole life is in the military and so gets regular checks, all of which say he's clean. I know I can't rely on this and I need to get tested myself, and I have booked a test. I just don't understand 1. how I could get it if he is clean, and 2. why my symptoms would go down while I'm taking UTI antibiotics if it's not a UTI. Has anyone ever experienced something like this? It's so strange to me đŸ˜•