What Causes Persistent Nausea, Headaches And Back Pain?

For the past 13 days I ve had bad nausea but never throw up, headaches(not every day) , back pain, tiredness, gas, and I ve had more mucus. It s not in my nose though. It s behind my uvula. Also in relation to the tiredness, my body is very tired but when I go to bed I cannot sleep for 2-4 hours. What does this mean?