We were a little warmer on this side of the lake today, but even so, I don't consider -5°C that cold. (And I ignore wind-chill in the forecast, since I'm always making my own.)

If I had that much stuff on, I'd die from the heat. Two balaclavas, plus a thinsulate bandana? It was -2°C coming home tonight and I still had on a summer-weight cycling skullcap under my helmet. Had I been riding further, I would have worn the winter-weight one. It was really a borderline night in that regard. ADDED: It was about -3°C last winter when I took my avatar pic in the middle of a three-hour ride. I'm wearing the winter-weight skullcap there.)

Everyone is different, of course, but I'm wondering if you're overdressing--especially since you're asking about sweat from your head making you cold. (The answer to that one is a resounding YES!) Otherwise, could it be your goggles don't fit quite right?

The rule of thumb is to ignore your mom's warnings and your knee-jerk reaction to dressing for winter. (It's my third winter and I still have issues in that regard.) You should feel chilly when you first step outside. You should reach a comfortable equilibrium between miles two and three, or 3–5 km. If you're warm before that, you're wearing too much.

Sweating is to be avoided if at all possible. It's easier to warm up if cold (pedal harder.) Sweat will lead to hypothermia.

Running just a bit cool (not chilly and certainly not cold) seems to work best for me. I carry an extra layer with me just in case I have to stop and fix a flat or something.