I hope you don’t have that light wired into the pressure switch on 240 volts? Otherwise I don’t know why it is only lasting a week. But even if you get the short life of the bulb figured out, light bulbs always go out when you really need them, and the pipe freezes before you know it happened. Also I have seen many a well house burn to the ground because of a light bulb being used for freeze protection.
Something like an oil filled type electric space heater is better, because it doesn’t get hot enough to catch things on fire.
I prefer a “pump house heater”. I get them from Grainger for a little over 100 bucks. They have a thermostat that works at really low temps, no fans to clog up with lint, and they don’t get hot enough to catch things on fire.