Sorry you are not feeling too good. I think you mentioned you were feeling nauseated. Have you been eating enough? Often times when I do not eat enough because of nausea I feel weak,shaky and lightheaded. Try to eat several little meals.
Also when I was in high school I was iron deficient (borderline anemic) and I would feel nausea, lightheadedness, weak, and shaky. Have you had a blood test on your iron? Don't worry this will pass. And if it is iron deficiency that can be easily fixed with iron supplements and lots of leafy greens.
I hope you feel better soon.
Vivs