I Have Been With My Partner From October 2014, On

i have been with my partner from october 2014, on november 25th 2015 i was tested positive for chlamydia, my partner tested negative in sept for STIs but i have been 100% faithful i have never been tested before for an STI and I'm wondering if i could have had it before our relationship and not pass it on until after her negative result or i their a chance that her test was a false negative?