how long does depo shot actually last? could I be preggo?

Ch

so I've only had two shots and was supposed to get my new one the 14th (was actually getting them the 25 of each month) but decided to switch to the pill because of side effects. I hadn't started the pill yet but we had sex the night of the 14th, could I be pregnant from that or was I still covered? from what I've searched online it's not a definite 12 weeks. it can last 10 to 12 weeks. I'm happy if I am pregnant but we aren't trying right now.