Good Afternoon.. I Wanted To Know What Is The Reason

Good Afternoon.. I wanted to know what is the reason that someone can come positive on a Chlamydia test and the other person negative. I always been tested and I always come negative on my results. Until I got with my partner the first time I was having vaginal disscharge and they tested me and i came positive on chlamydia they treated me and everything. Now I was having some bleeding during sex intercourse and I was done some testing and my OBGYN call me to tell me I was tested positive chlamydia. How is that possible if I was tested and treated the first time. My partner was treated and I was treated this time. His results came in and he is negative. I do not understand why I came positive two times and he came negative on that. Can this question be answer to me please?