I always tell to the students, it is not branch but it is you who has a future. What ever branch you will study, successful career depends upon you and not on your degree. You don’t have to listen any body for selecting the branch, except your parents. You should listen to their views and discuss your likings.
For becoming Psychiatrist, you need to be doctor first. (You should complete M.B.B.S. and thereafter have to do M.D. in psychiatry)
To improve your mental control you need to do physical as well as mental exercises like meditation, autosuggestions etc. Prioritize your task and get after one task, one time.