Depression's so tough, and the sudden intensity of it surprised me with this quit. I hope the wellbutrin helps. But there are things you can do to fight it above and beyond medicine (which will address the chemicals, but not the problems).
This is what works for me: Allow yourself to be sad, but try to allow yourself to be cheered up, too. Even if you're depressed, try not to think constantly about how depressed you are. If you must obsess, find something to obsess about. Find a project, something you've always wanted to learn or do or try. Try to get out and try to have fun.
Don't give up on feeling better, but if you do, just give up for a day. Wake up the next morning and try again.
The thing about low self-worth thoughts, is you can do something about them, because really, you're not the scum of the earth to the nth degree. Do something that makes you feel good about yourself. Put on your nicest outfit, and acknowledge that you look sharp. Do something kind for the people you love. Buy a lady in your life flowers. Take a sick day from work (mental health counts too), and go walking in the park, go enjoy the world. (It's a beautiful world, and it's even more beautiful as a non-smoker, because you're not nastying it up with your smoke and cigarette butts.)
Address and confront your worries, or they'll eat at you. Get your vehicle serviced. Review your finances and make the changes you need to. Do whatever you can to ease the worries plaguing you, so you feel less overwhelmed and more empowered.
A pro-active approach to depression won't cure it, but it will help you avoid the scary parts. And pledge to yourself that never, not ever ever, will you harm yourself. If you do that, and you believe it, you'll feel less scared, and you'll feel better.
Good luck. Rooting for you.
Adrienne