I have post nasal drip and have sneezing attacks in the mornings, it seems to be worse if I eat any sugar or empty carbs. For me I have what seems to be allergies. There are many people on this board educated than I am. I just try to notice what is going on with my body.
I tend to sleep flat on my back because of neck problems, I have a sore throat from sinus drainage most mornings.
My daughter sleeps on her right side, when she gets an earache it is usually on the side she sleeps on. She had mono a few years ago, I keep a close watch on her. Her energy level has never been quite the same. She does not have CFS.
Warm damp compresses in the morning might help some. On that left side sinus and ear. If you live in a cold dry climate, try a humidifier at night.