The thing that is making you stress is that you are giving yourself no free time.
Get out there, take an hour out and drive (or walk) around for an hour, clear your head and just enjoy senseless calm without having to worry about anything.
On the other hand, once you start University, you will have so much free time (depending on the course) and you will make amazing friends and meet unbelievable people that will stay with you throughout your life!

Conclusion, don't fret, it's not unusual. Just give yourself some time, play some games, walk, talk, go annoy your siblings (if you have any) to just have a little laughter.

Laughter is the most important thing to a human being.