I got chlamydia 4 months ago..

I dated a guy for almost 2 years and in April we broke up and in the end of May I started dated my current boyfriend of 6 months. I went to the dr and found out that I had chlamydia.. The dr said I didn't have it for long so I automatically thought my boyfriend now has it but he got checked and he doesn't have it but they gave him treatment still. I contacted my ex and told him and he said he got checked and he doesn't have it either? I had it and don't know how I got it? Is my ex lying.. They both have had it before. And my boyfriend still never got it even if my ex did give it to me without me knowing? How is this possible? I haven't been with anyone else!