Help?

I went and got tested on the 21st because I thought I had a yeast infection and it turned out that I have chlamydia. I've only been with one guy for the past 4-5 months and I was his first. The last time before this that I had unprotected sex was a year ago. So my question is.. is it possible I've had it this long and have not known? And when does this STI start affecting fertility.

(Before anyone says anything I was given antibiotics for my parter and I)