Ur described symptoms indicate toward few conditions like anxiety, depression, over mental stress etc.As attention is also poor its reflected on ur studies and memory. May be a deep emotional disturbance is bother u. I think it is hightime to consult a psychologist offline or Online for ur problems. With psychotherapy and counselling u will surely get help and learn how to deal worse situations in life. Best wishes... Feel free to contact..

Try using study skills You seem to be having attention issues. Go for behavior therapy which can help you overcome your problem

It shows the lack of clarity about yourself and your future. The purpose of life will make enable you  to have focus in your life.

If there is anything in particular worrying you it's better you talk to someone or jot it down and figure out what to do with it. Fix timing to study say 30min in that time tell yourself u will think about anything else after 30min.take a break of 5 to 10min and repeat the same. This way you know you have to put your 100% in that 30min