i was just diagnosed with chlamydia?

I've been in a serious relationship with my gf for 7 months. We are very serious and very sexually active. We do have unprotected vaginal sex but that's it she's has a iud so it's unprotected. I trusst her with my life and I do love her she isn't hiding nothing or acting suspicious. I've been having weird symptoms lately and I was diagnosed with chlamydia. I never had an std before she claims that she hasn't either. My previous relationship I always used a condom so the relationship I have now was the first time I had sex without one. I asked her when was the last time she had sex with someone else. She had sex with her ex 2 years ago before they broke up. How can I get chlamydia in a faithful relationship? We are very sexually active we have it almost everyday sometimes even twice a day