A fear of losing something or someone again for a mistake.

I don't know how to react in this situation but I really need someone who will help me. Help me to focus, to understand my real goals of life. Now my priority must be to focus on getting a job. But I am unable to study for the exam next month. I'm trying to engage all my nerves to prepare for the exam and at the same time I get disturbed without any reason , also without anyone besides. Day by day, that distraction becomes deeper and deeper. Today, also I started studying but was unable to concentrate more than 30 minutes. Suddenly a thought came in my mind. Why my friend is not calling me for long time. If I did any mistake again and for this no one is talking to me again. Then I started reminding my mistakes. Then I thought , may be I did any mistake and I got forgotten. I knew it better that, I didn't forget anything. But I felt like, my brain was continuously telling me .. "You did a mistake again, so no one is talking to you. Also you forgot your mistakes." I tried my best to remind everything but was unable to convince my brain that, there is nothing wrong I did and got forgotten. Why is this happening with me? I was not like this before , then why now? Am I getting seek? Am I getting mad day by day? How can I achieve all my dreams with this weakness of my mind?