How should I deal with congestion before bed?

Before retiring, take a long, hot shower. Breathe in the steam. Have a cup of tea, hot cocoa while you sit down in a relaxed mode. Try to find something decaf. Take a cough suppressant, something like Mucinex DM or Robitussin DM, Nyquil etc. Get into bed with a good book. You'll feel better the next day and you won't have to do this beyond when the infection clears. Of course, you have allergies so you'd have to decide when to stop. Although, I've found, that it's a good inducement to sleep. If I'm better rested I can go about my day with a much better attitude.