I agree with lilwing.
Your personality changes as you experience different things, because it is those experiences that teaches you and makes you see things differently.
I used to be shy, and I have almost overcome that - I'm more daring, I will talk to people if I want to and go wild on the dance floor (I often feel at home on the dancefloor now) whereas before, I'd be quiet all the time and never speak unless spoken to - but my experiences helped me to change.

I think if you made a list of who you are (what characteristics you have) and what you want to become, then that would be a start. Once you have your list, think of actions/things you could do/think in order to be more like the person you want to be.
If you want to be more positive, many people have that typical post-it by the mirror saying something like "I am a respectable, good-looking person who is good and kind."

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""The best love is the kind that awakens the soul and makes us reach out for more. It plants a fire in our hearts and brings peace to our minds."