Praise be to Allah.
The issue that you are complaining of has to do with your personality type and is not regarded as a true psychological disease. What is needed to treat this problem is the development of social skills, which can be done, but it requires persistence, patience and ongoing social training.
This training program may be summed up as follows:
1 – Preparing yourself intellectually, mentally and physically to mix with people, put up with them and try to be in harmony with them as much as possible.
2 – Playing any kind of team sport such as soccer – for example – which involves some kind of conscious and unconscious contact and interaction.
3 – Joining charitable and voluntary associations, attending Qur’aan study circles and halaqahs (circles of knowledge).
4 – Try to visit a trustworthy psychiatrist who can tell you some useful ways of dealing with this problem.
5 – Avoid feeling isolated from society. Try to forget all things that exacerbate these feelings in you, for the cause of this introversion may be a situation in which you found yourself or a trial that you have gone through. Seek the help of Allaah in dealing with it and forgetting it.
And Allaah is the Source of strength.