Hi. Your description of statement shows that you are depressed and had some bad experiences in your life. These emotional outburst will lead to feel useless to everyone. Seek the help of psychologist. So that just in few sittings they will help to overcome Ur situation. They will remove the negative thoughts in you. If these issues are corrected then surely you will be able to concentrate in Ur studies. Never lose hope. People are always there to help you. Also Ur stress has to decreased. You can also come to me if you feel comfortable.