I can't concentrate on my work or study.

I have never thinked of it before, but i realised it might be an issue. I was good in school, but by time my acdamic performance became poor, after that i couldn't concentrate on reading long like more than 5 minutes. How bad i try overthinking won't let me concentrate. I feel very frustrated most of the time. I react to a normal talk very aggressively if it is against my opinion. I get very emotional often, how bad i try can't put a decpline in daily schedule. I couldn't complte a task even which i started for a greater sake. My mind diverse always, i am impatient some time. Decession changes always, i hurt my close/family by saying foul/emotional words even i didn't meant to. I always realise that i have done so bad, shouldn't have done that. I feel depressed, can't even continue a daily schedule, on the 3rd-4th day i always forget or break the rule. I feel hard to remeber something which i studied a week ago. I am always thinking something unearthly. Help me!