Firstly I really appreciate that you actually admitted your weakness in an open forum. Very few people can do this. You actually deserve appreciation for this.
Lack of confidence is a common problem. Some are less confident and some are bit more. The first thing is tell yourself its ok to be unconfident, its ok to be imperfect, its ok to make mistakes and its ok to fail. As no one can be perfect. Everyone has their weaknesses. So don’t be too harsh on yourself. There is a lot of people around you to do so and to pull you down. Accept yourself as a good human being with all your strengths and weakness and then go ahead with improvement. Some points which can help you are :_
1. Every morning stand in front of mirror, smile and tell yourself. I am a good human being so I am better than many others who are bit inhuman, selfish and arrogant. This will let you believe in yourself. Smiling will make you accept what you said to yourself. It will make you feel good.
2. Pray to God to guide you through the day so you are in his protection cover and it will be easy for you to move ahead with your mission positively.
3. Make a list of things you are good at. And things which you cant handle properly. Positive list will make you believe in yourself that you can deal with the negative ones.
4. Do things which you are good at. The appreciation you will get from people will rise your confidence.
5. Read motivational books. Watch movies like Choti Si Baat and Anand
When you write your exams stop studying before 10 mins of exams. Tell yourself that you are done with your lessons. The questions may not be from what you studied but you will definitely know the related topics and you will manage with flying colors.
When your subordinate is near you take a few seconds drink water and tell yourself that you are sure about what you are typing or doing. And ypu will do it well. This may take time but it will work. All The Best.