Also along the lines of global warming you could talk about environmental problems like using cleaner energy like solar panels and why we don't use more of them in places with more sun exposure like deserts that could give us more power
I put a shadescreen on my patio door.
The difference between being sick and feeling exhausted is that when you're sick, there's a virus involved which causes a disease and makes you ill.
Feeling exhausted on the other hand is slightly different. You feel physically or mentally drained due to overworking, stress and exercising.
Public school is a fairly different change from private and home schooling but it's nothing to fear -- there are a lot of different people there which almost make it impossible for you to not click with someone or even a group of people. School shootings are sadly much more common these days but i'm sure your school takes certain safety measures in hopes of preventing any sort of occurrence that could put you in danger. There are certain freedoms of public schools that you should take advantage of and enjoy especially as you near your high school career, give it the first week and i'm sure your find yourself enjoying it! :)
The answer is flexible hours because flexible hours are what your sentence is implying.