Oops?

So I had my depo shot on the 30th of September. The nurse told me to wait a week before having sex, unless I used condoms. As soon as I got home, my fiancé and I had sex. I mean come on it was my birthday. Well of course he released a HUGE load in me. Our baby will be 2 months old on the 19th of this month and he doesnt want another child. I've been having some weird cramping but no period. Could I be pregnant again? If I am, how am I going to tell my fiancé? I am going to test next week, but could this be implantation cramping? Please no rude comments.