If you aren't familiar with feeling good about yourself then once you do feel it you might experience some discomfort. You see we are comfortable with only what's familiar.
It's possible that feeling good about yourself might be very uncomfortable because it's an unfamiliar feeling. But consider this an exercise to do in baby steps.
Sit in a comfortable, quiet place. Inhale slowly to the count of 3 and exhale slowly to the count of 4. Do this three times.
Then imagine yourself in a situation you might have experienced in your life, no matter what age, when you accomplished something or felt happy, or received some praise. Anything when you might have felt good about yourself.
Get in touch with that feeling. Where do you feel it in your body? Can you get a picture of that feeling in your body....is it a sensation that tingles, does it make your chest expand, do you feel it in your gut.
Do not judge the feeling. Just notice it. Try to stay with it as long as you can, as long as it isn't disturbing you.
Do this whenever you have the opportunity to get away from any distractions, even if only for 5 minutes.
Getting used to feeling good about yourself will take some time, if you haven't felt it often enough or even recognized it when you might have felt it.