What do people mean when they say I have "no personality "?

It means you have not learned the social skills. They will not change even if you take the trouble to learn some skills. Change is worse than anything else. So you need to take acting classes to learn how to act in public, and then you have to find all new friends who didn't know you before you took the classes. The bonus is that acting skill will get you a job offer even when you are not qualified for it, and vocal skills will improve your earning potential more than any other detail. Get "Dress For Success" by John Molloy.