Hi Michelle, I know it is unnerving, believe me
I went from probably 14 years of normal paps to severe dysplasia which ended up turning out to be a surprise microinvasive cancer diagnosis. I know the questions that are running through your mind, really I do. I could tell you horror stories that ran through my mind. But the chances are really really slim that he has stepped out on you.
Having a baby really throws everything out of whack, hormones, everything. It takes up to a year to go back to "normal" after you've had a baby. So hopefully, this is what is going on. A good reminder though to keep up with the smears, which I know you'll do.
Hope this helps a bit.