HVAC design is my day job. I'm guessing that you've been heating your house and you have a heat pump? If so its likely that the heat pump is not coming on or your thermostat is set to "emergency heat" which just uses an electric coil like a space heater. Those coils use a LOT of power. I'd check there first.
Thank you for the insight.
I do have a heat pump and it seems to just run continuously. The auto function doesn't seem to do anything. I set it at 73, and the thermostat eventually shows 73, but it never shuts off. The house has baseboard heaters as well, which is what the previous owners used. It seems like they knew that the system was messed up, but never bothered getting it fixed.
I've been looking at the energy usage, and the only days that are reasonably low are the days I didn't run the heat at all. It's been off for a couple days and usage is way down.