Hello there!

Greetings!

There's no need to worry you can improve your concentration power , first of all as your concentration power is low you should not seat for long hours for study , rather you should study in small sessions of 1 hour and after each hour take  a gap of 10- 15 hours so that you don't get bored and lose your concentration power and you should mix the subjects you study I mean if you don't like physics then first read physics for 1 hour then take a break and start with biology and after an hour again start with Physics . Also you can use nmenoics as well to learn things and facts as well and whatever you study you must revise it at regular intervals.

Thankyou