Definitely agree with 'rain'. Sadly I know this is about your low self-esteem, cos I was like you for many years of my life. Even though I can look back now and see that I never was ugly, I did'nt believe it at the time and wasted so many years feeling I was'nt good enough.
What a shame, and how horrible you must feel. I know there is no amount of reassurance I or anybody else can give you, because until you learn to like yourself, it wont mean anything to you.
I can only assume that when growing up, you were not given much positive affirmation that you were a worthwhile human being, equal to all others on this planet!
After many years of feeling hopeless and inferior, I finally realised that this was only because my mother was highly critical of me, and never encouraged me or gave me any praise. Knowing this has enabled me to learn that I was good enough, and always have been, its just that I BELIEVED that I was'nt.
Now I quite like myself, and am kind to myself, and feel so much better about life in general.
The other day I saw a video of myself 19years ago, and remembered how much I disliked being me back then.
Its a shame to waste your youth feeling so horrible, trust me I know.
Only you can start to learn a different way of feeling about yourself, and I hope you get there before too long.
Do try and see a counsellor if you can, it will be a worthwhile investment in yourself, and hopefully save you further years of pain and sadness.