You've pretty much ruled out a defective regulator and a pinched line.
One possibility is your tank contains butane, not propane, which stops "boiling" at about 32 degrees. Butane works fine in the summer, but not so well in cold weather. LP gas has to turn from a liquid to a gas (boil) for it to be available at the appliance. Propane boils down to a way down below "0".
Several vendors in the south sell butane or a mixture of butane and propane. You may have used all of your propane up and now only butane is left.