How can sedentary lifestyle lead to sleep deprivation

Because without physical activity, the body has extra "energy" if you will, and so when it is time for bed you are not tired, so you end up staying up all night. also there is probably an effect on your internal clock, which messes with your melatonin production which goes hand in hand with your sleep cycle

Each gram of carbohydrates and proteins yield 4 calories / gram . the more the calories a food has the more energy it provide to you body.

Maybe meditation,stress relievers,try to have quite time try to get school done on time and try to go to bed earlier