Can someone please tell me if I'm being really stupid or not?😳

I've been getting the depo shot for a number of months now and ever since my second shot my periods stopped completely not even had any spotting nothing! And I've been getting my shot on time every time. So does this mean I 100% won't get pregnant if I was to have unprotected sex? Since I'm guessing you need some type of period to at least get pregnant??Â