When you have a cold or the flu you should prop your head up higher than you normally would which helps your sinus pressure drain off and helps you feel better and breathe better when you have sinus pressure.
Sinus pressure gets better when your head is higher than your body so elevate your head higher than you normally would when you sleep to allow gravity to help relieve the sinus pressure.
I would also recommend eating some hot soup and drinking some hot tea with some honey in the tea which helps relieve congestion and sinus pressure as well.
Taking a steamy hot shower or sitting in the bathroom with the shower steaming on as hot as you can get the water can also help with your cold or flu and help you breathe better.
Using a vaporizer or humidifier in your home or bedroom when sleeping also helps you breathe when you have a cold or flu.
Be sure to get plenty of rest and drink orange juice or other juices with Vitamin C and eat Vitamin C foods to help boost your immune system.