Welcome to Health Care Magic. Thank you for posting your query.
I can understand your concern.
It's good to know that you are a happy person. At 15 you should be.
Now , coming to the extreme
fatigue part.
This fatigue is due to the lack of physical activity.
After coming back home , take a nap for about a couple of hours.
Go out in the afternoon either to play cricket ,soccer or any other outdoor sport or walk or jog. Do some sort of physical activity . By doing this , I am sure you will feel fit and fine.
Come back home , have tea , study for a couple of hours . Go to sleep at around 10-10.30 pm. There is nothing to worry. Do some physical activity.
You will get over this quite easily.
Hope this helps.
Post any other question. We will be happy to help.
Have a nice day. Regards.