Thanks everyone for your help with this, I had no idea where to even start looking, but after some of the responses I got, I was able to locate the problem!

As soon as I looked under the hood, by the Master Cylinder, I noticed that the check valve on the brake booster vacuum hose had completely broken in half. I ordered the part the other day and expect it to come in any day now. In the meantime I was able to temporarily fix it with duct tape, to ensure no vacuum loss, and now I have brakes again.

Thanks again!