Pregnancy after vasectomy.

My hubby had a vasectomy in Oct 2014. In Jan of 2015, he got the all clear, saying he had a zero sperm count. Earlier this year, (May) I missed my period and was 27 days late. Then I finally got my period but it was really heavy and painful. Then I had three normal periods (July, August, and September.) Now my period is five days late again. What's wrong with me? I doubt I'm pregnant because he's unable to reproduce but idk. Maybe God has blessed me. (Fingers crossed!!!)

PS, before anyone comments saying that I shouldn't want a baby against my hubbys wishes, I'd like to say that he got the surgery to prevent another child, yes. But he has told me that if it happens, he wouldn't be mad. I think he actually kind of wants a girl. We already have a five year old boy.