I am preparing for IITJEE 2015 ,n m fucked up  ,i am suffering from lower back pain (cause / solution unknown) due to which i cannot sit for more than 90min at stretch, then i need a break for 30 min, but the 30 min break turns out to be 1 and half hour break ...i dont know how to manage things ...P

You, my friend, need to start exercising - remember - health comes first! And 90 minutes is a decent stretch - take that 30 minute break and in that time - go outside and take some fresh air...that should help..also, make sure you sit in a comfortable posture and do see a doctor!

I'd advice you to pay a visit to your doctor and get it checked. It's a matter of your body, and body comes first than anything else. Also, ask your parents for some help. If you stay alone wherever you study, call up your mom and then tell her your problems. And Best of luck for your JEE. Maybe, we both will meet one day in some IIT, cuz I'm also preparing for JEE 2016.

Lower back  is much sensitive area . science and doctors themselves cannot answer and predict your problem even today  in many cases.Human back is too complex I was having the same problem and still persists some time. The best solution is to do exercise but gently not do overexercise and must do after warming your muscles(do yoga 5 to 10 minutes then do exercise or do walking one must not do exercise immediately after waking up). eat fruits specially banana and other fruits which has large amount of calcium,Use pillow to seat (Take pillow with you where ever you go). Health is real wealth . Else thing you can do is try to generate endomorphisms .They are natural pain killers generated when you laugh ,one you cry,acquainted with feelings deeply of love to-words your self.Motivate your self by reading books if you don't have time just watch 2-3 minutes inspirational video daily. Just create quote of your own to fight against back. If you are having muscles problem it is one day going to leave you. Good luck wish you all the best

Firstly consult a doctor get an X-ray  sort your back pain problem ask you mom and dad for help. You can also try some yoga methods to avoid back pain. Try to increase your study hours as sitting 90mins at a stretch is not sufficient you must be used to for at least  3 hrs. Go for early morning joggings as that refresh's ones mind. Now for studying refer to some good books start solving mentally, scribble more , practice more. Everything will be fine  you will be alright and defiantly crack JEE . ALL THE BEST .

Frankly, I never sit and study. Seems too much of an effort. Always found it easy to lie down and read whatever it is as if it were a novel. Always found it relaxing and easy.(I can't say it works for everyone though). When it came to solving questions, i did that as if a heroine was writing a love letter in indian movies(lie on bed, face down and solve it). 30 mins break, i cant offer much advice there. JEE prep is really boring and i dont blame you for taking extended breaks