I have the flu and can't breathe through my nose

You may also do this already, but I find with a cold (both pre-CPAP and since I started CPAP a month ago, as I've had a cold since then) that propping my head and shoulders up a bit using two pillows and laying on my back helps with the congestion. I normally can't sleep quite as well on my back, and I know AHI events are more likely, but sometimes you gotta do what you gotta do. Even turning eventually on my side, being propped up a bit helps with the breathing.