What Causes Mucopurulent Cervicitiis After Having Protected Sex?

I have MPC but I was clean before my boyfriend and I were dating cause I took Pap tests and others to make sure. I haven t slept with anyone since that test but with one person but we used a condom and I am pretty sure it didn t break. A month after I met my boyfriend, I have been with him for 6 months and the symptoms of spotting and discomfort with sex started last month and we both did not have sex with anyone else and we are both positive that we were clean. How did I develop this? How long does it take to see symptoms from the time of being infected? We are both puzzled and its affecting our relationship cause he thinks I slept with someone else. I did have a yest infection last month too.