Everytime I lay down, especially on my stomach, I get nausea. Why is this happening?

Improve nausea. Nausea is a sign that something is irritating the stomach. This can come from sinus drainage, medications, food, gastritis, maldigestion, slow stomach emptying, pressure from other organs around the stomach, gall bladder issues, and pregnancy. See your physician to help figure it out but keep track of your eating habits, anything that helps it or worsens it.