STD Question Ladies Please Help

So I was diagnosed with Chlymdia Dec 16. My boyfriend and I took the antibiotic that Same day. I waited 6 weeks to get retested and it came out positive again. We had sex one week prior to getting retested but we used a condom. So the doctor gave us another set of antibiotics, I go back in two weeks to get retested . I'm very worried. So My question is why am I still positive?