Thank you for writing. It may be that your mother’s words created what’s called a “self-fulfilling prophecy.” You were told from an early age that you couldn’t do anything. Kids believe the grown ups, so you accepted the judgement. The result may have been that either you didn’t try or that the normal mistakes that come with learning anything new became proof in your mind that she was right. The less you tried, the more incompetent you became. The same thing may have happened with social skills. You already believed that you couldn’t interact with others so it’s possible that you stopped trying, which resulted in not learning what you needed to know to be comfortable interacting with others.
Fortunately, anything that is learned can be unlearned. You are good at studying things so now you need to start studying people. Take some time out from trying to socialize in order to give yourself some social skills lessons. Pick out some people who are comfortable socially and watch them carefully. Listen to how they manage conversations. Observe their body language. I’m not suggesting you be a stalker. I am suggesting that you are around people every day who know something you don’t about getting along with others. You can learn a great deal by paying attention.
Similarly, take some time out from trying to fit in with sports and get yourself some lessons and take time to practice. You didn’t mention if your father is in the picture so I’m guessing he is not. But perhaps you have an athletic relative who would be willing to teach you about a sport. If not, consider talking with a coach at school about giving you some private lessons.
Another alternative is to find a sport where you are on a team but mostly competing with yourself. Swimming and track or cross country running, for example, are sports where the object is to improve your own time. They are also sports where you can practice on your own.
You are a smart young man. Social and athletic skills will not happen like magic. But they can happen with self-discipline and practice. Your mother is wrong. Her comments haven’t been at all helpful. Now that you are in your teens, you are less dependent on her and more able to judge things for yourself.
Take charge of your own social and physical education. Give it a year of real effort and things will be different by this time next year.
I wish you well.