Please don't beat yourself up over this. You have an illness. You're not lazy or defective. Your brain just works differently.
With help, you can get better. Please don't give up. I know what it is like to be very depressed, and see no hope. Then I stumbled across a medication that really helped with the depression.
As someone with bipolar, you probably want to avoid antidepressants, especially SSRIs. I was on prozac, and it really hurt me, even though I took a mood stabilizer with it. The good news is that there are medications out there that act like antidepressants without actually being antidepressants.
Have you tried lamictal, lithium, seroquel, zyprexa or abilify? Zyprexa is the drug that helped me so much, though it has some nasty side effects.
Please don't give up hope. Some of the best moments in your life haven't even happened yet; hold on.