If im 200% i didnt cheat, and she said she's 200% she didnt cheat.How did we get chylmydia?

We been with eachtoher for 5 years. I swear on my life that i never cheated or have any type of ual s with anybody. We have two child together. One is 4 and the other one just turned 1. The first child, going through all testings and etc, everything came out to the clear with no std that can be transfered, nothing at all. Even before, i paid hundreds of dollars getting tested, for every diesease or std you can name. I ran all blood tests, urine tests, having the doctor looking at everything. I was 100% negative with any STDs.I love this girl dearly, and i would die for her. Relationships has their up and downs.Everybody knows that. But here again, she was pregnant with my second baby. I guess they do testings and all them check ups etc. She came and told me that she has Chylmydia and starts crying, and was stressed out for several of days.At first she didnt tell me, she stayed quiet, and saddened to herself..Then told me that i had to go get checked and take anti biotics?? I said for what..she said i have chylmydia.At that time i do not know what that is..So i went to plan parent hood and got checked and the doctor told me that neither me or she slept with multiple partners??? I swear on my Life, if i did cheat on my wife, i will let god struck me in the heart by lightning! I asked her several of times, she said she never cheated on me or ever had with anybody..How did we get it? Is there any other way of getting it? How come she didnt have it with the first baby that was 4? Why she has it now with my second baby? Im so confused.I love this women, and it confuses me everyday, hurts me everyday to think about it. Please who can i go to to get more FACTS, who can i talk to, TO KNOW THE TRUTH!