If the car was serviced in November I wouldn’t expect it to be very low on oil in such a short space of time. Sensible way forward is to buy a 5 litre pack of the correct oil, top it up and monitor the level. Check for obvious leaks or drips on the driveway, there will be a simple answer to this conundrum. Possibly the right quantity of oil was never put in at the service?

OP needs to have a look under the car with a torch and see whether there’s anything that looks distinctly oily.

Took this thread as a prompt to check wifey’s Focus, sure enough it needed topping up.