Sorry to hear you're feeling so down, Wook.
I've struggled with depression since I was a teenager, and resisted taking medication for years, as I thought I should be able to 'pull myself together' and snap out of it. I know all the things I need to do to feel better, it's just that when I'm depressed, I can't do them. I've finally come to the conclusion that, for me, it's a chemical imbalance, and I take the medicine to correct that as I would for any other condition. My doctor told me that she finds it odd when people feel they mustn't take anti-depressants; they would take the medication to control diabetes, why not depression.
Having said that, I think people get different kinds of depression, for different reasons. Endogenous depression is when the depression 'comes from within' - you're depressed regardless of 'having nothing to be depressed about' or everything in your life being fine. That's what I have. Exogenous depression, on the other hand, is when you become depressed following life events such as bereavement, redundancy etc. You could term exogenous depression as a natural and valid reaction to difficult events, and it can also be a signal to you to take action and make changes in your life. In that scenario, I don't think medication is particularly helpful. Then, of course, there's PND, which as people have pointed out, doesn't always kick in until your baby is older.
If you have an understanding GP, it's probably worth having a chat with them; it might be that a course (say, 6 months)of anti-depressants would give you enough of a boost to set you back on track, or that there are other measures you can take that will do so. If you're uncomfortable with ADs, consider herbal medicines too; research shows good results for St John's Wort.
Mainly though, know that you're not alone, and that there are people there to listen and help you. I've felt, many times in my life, that I didn't want to go on any more, but I'm very glad I did carry on! It's so hard to see a way out when you're in the maze of depression, but I promise you there is one.