hpv..pregnancy..confused

ok so I went every year to my obgyn to have my annual and still do. I'm constantly making sure I'm healthy and nothing is going on. I have never had an abnormal pap until I was pregnant. when I was pregnant I had 1 abnormal pap and my doc said I had hpv.

how could that not be picked up before? also now that I have gave birth I haven't had any abnormal paps and was told I don't have hpv...

how is this possible?