Being negative about myself is something I do very, very well. I've been doing it for as long as I can remember (say, the mid 1980s - maybe somewhere between 1984 to 1987. I was only born in 1980). I go through times thinking I am the most useless, worthless person ever.
Why do you think you're useless and worthless? Sometimes I'm intensely harsh on myself too...I'm my own worst critic. However, though I've only known you for a very short time, judging from your posts, you sound like a kind and intelligent person to me.
(By the way, we're close in age; I was born in 1983.)
Remember what McCoy told Kirk: "In this galaxy, there's a mathematical probability of three million earth-type planets...and in all the universe, three million million galaxies like this one. And in all of that, and perhaps more, only one of each of us. Don't destroy the one named Kirk.