Hi I'm a 16yr old boy.I m good in studies.everyone says that my mind is sharp and I also know that but when I sit to study I can't concentrate.is this happens due to girlfriend or friend or something else.please help me out from it.

Poor concentration can be from many causes. One is stress or having something else on your mind. Grown ups have that experience a lot. Another possibility is a hyperactive ADHD type disorder but you would have know that way before now. The other possibility is that you don't like the material you are working on or the subject(Don't tell your mom I said that). Things like being overly tired or not feeling good too. Think about what is going on when you have these periods and good luck.