Brake lights went out

A couple days ago the brake lights stopped working, but they turn on when the headlights are on. so I checked the fuses, they were good. So then, I got new bulbs, put those in and they still do not work. The bulbs all turn on when I turn the headlights on so I am at a loss. I researched and found that there is a switch under the gas pedal they may be loose or need replaced. Could it be that I need to replace the bulbs in the back window too, just wondering if that would effect the the brake lights? -Hannah