Pregnancy after vasectomy?

Can this happen? I'm freaking out! My boyfriend had a vasectomy 4 years ago now (no way he lied about it or anything, I drove him too and from the appointment, and took care of him when he saw his little wounded balls and fainted. It definitely happened.)

My period is 9 days late. I tested after a week and it came back negative, but my very punctual period is still not here. My boobs hurt and I'm eating twice what I normally eat. I'm always starving recently! I had a little bit if pink spotting around when my period was due...

Freaking out.