First of all,don't think of it as 'stress'.Consider it as an activity that requires a bit more attention than your other activities.(Believe me what I am telling you,I too have my class12th board exams next month.)
Secondly, make a time table for your studies and strictly adhere to it.And don't forget to give sufficient time gap in between.Utilise that time in the activity you love, maybe kick some moves if you like dancing or perhaps listen to a few songs you like.This will help you come out of the book thing.(I know you must have heard this already but believe me,it helps.)
And lastly don't you ever keep yourself locked in your room among the piles of book.This can really create negative energy around you and ultimately,will make you feel less confident.
Hope that's of some help to you. :)