In the 12th you were probably 6 years younger. That is a lot of time that has passed by and your mind and body is not the same. Even if it was the same, it is not advisable to study so much everyday. You need at least 8 hours of sleep anyway. You may also have some problems related to delayed adolescence to boot. First of all, the intensity of stress
is in the perception. Change your perception, there is no stress: it’s like looking at a glass half full or half empty. Apart from that, all your emotions need to be dealt with by expression i.e. You need to talk about the feelings. Then you need to exercise regularly, eat fiber foods (whole grains, fruits and vegetables), sleep at least 8 hours every day, learn Yoga and meditation
, learn stress management, and do a personality development course. Because you are into studies, follow a tight schedule, with good breaks and study habits. If group study helps you, do it with the right people. If tutoring is required, arrange for the same. These should see you through successfully without the stress.