I find it difficult to concentrate and get sleepy, when I start studying. What is wrong with me?

Hi doctor,

I am a student who is currently preparing for a competitive exam, and I am feeling very low and have a lot of negative thoughts. I have a very good family, who have fulfilled all my wishes. When it comes to my studies, even my parents never forced me to study more than my capacity. All through my school and college, I scored more than 80 %. But when it comes to solving analytical questions and quantitative aptitude, I am very slow when compared to other people. Right from school, I have this tendency to solve the problems slowly or make a lot of mistakes. The worst part is, from childhood my brain has not matured in how to solve a problem through critical thinking and applying the skill, that is very much needed in mathematics. After graduation, I got a job, which I was not happy with. After working there for almost a year, I got frustrated with the work, as I was not learning anything that I expected. I love coding and learning advanced stuff visually. I am always in mind to achieve great things in studies and job which many people are currently doing. I thought if they can do it, then I too can do it. I resigned my job after a lot of thinking for many days, as money does not matter to me, but only learning does. When I try to do anything that I believe is great, then I tend to get lazy. I prepared a lot for the exam, but I scored a very low score. I am shattered as my hard work is wasted. I am preparing for the exam a second time, and I am again feeling lazy. The thought of getting a low score is affecting my preparation now. I get distracted by web browsing and TV for 1 to 2 hours. As I stay alone, I feel very sleepy and drowsy. I think my brain is converting all the ATP into ADP, and I sleep off for 3 to 4 hours, after studying for a couple of hours. Whenever I try to concentrate, all the negative feelings are coming to my mind. But, I motivate and pick up myself, and study. I am very lazy and less energetic than before. It is like someone has stolen all the energy that was within me. Also, I am feeling lonely, I thought a little walk outside would help me freshen up. Now, I have come to a situation that when I see the books, I am demotivated and feel unhappy to prepare for the exam. This is the most important time of my life to prepare well and pick up my career, but a lot of fear and negative thinking is present in my mind. What is wrong with me?