How much can chlamydia affect fertility??

I went to the doctor to discover I have chlamydia and the Zithromax didn't cure( mainly because I had sex on the third day of treatment) I'm not sure how long I've had it, but I've ne cheated on my boyfriend and I can't bring up the topic or stomach the thought of him cheating.. Could I go get Zithromax again and will it work since I've taken it before?