Cheating on me...?

Hi. I just went to the clinic for my annual pap smear. I have the Mirena IUD put in six months ago after I had my baby. Since then I have been having bleeding after . At the clinic, the doctor diagnosed me with cervicitis after looking at some discharge under the microscope. He told me that I possibly have an STD, such as chlamydia, which could be causing this. Thing is I am married and according to my husband, he has never cheated on me. What could have caused the cervicitis, an std, the IUD, having the baby? Does it mean my husband cheated on me? Please help!!! I don't get my chlamydia results until two weeks so I am so worried.