It's really hard and honestly, I go through the same thing, except having another baby isn't even really an option for us, because of medical issues on my part (I had problems with blood clots after my daughter was born and I've been told that if I became pregnant again, between that and my age, I would be in the "high risk" category, and we've decided it's not worth the risk). Most of the time I am fine with it, since we had already decided for all the typical reasons that we weren't going to have more, but now our daughter (who is 4) is noticing all her friends have baby brothers and sisters, and she LOVES babies and thinks she wants me to have another baby too. And I feel so torn, because part of me wishes she could have a full sibling and I know she would be a fabulous helpful big sister. And it would be easier for me to have another one now rather than when DD was 2, since DD is now doing preschool, she's more self-sufficient, she's potty-trained, etc. But then I also am happy that, thinking back on the hardest things about babies (waking up at night, needing diapers changed, the toddler years, etc.), I am NOT going through that again!
Point being is, I think what you are going through is very normal. If you say you are depressed, or having feelings of depression, then you need to address that with your doctor, because I suspect that many women try to deal with their depression by having more babies. I'm not saying that's what you are doing, but for some moms, having another baby becomes their way of coping, because they always have another baby to look forward to, rather than dealing with their depression head-on and treating it appropriately.
You didn't mention your age, but to me having kids that close together would NOT work for me. You can always give it another couple of years and see how you feel. You can also always decide to adopt. That would be an option for us if we really wanted to, but unfortunately, DH isn't as on board with the idea as I am - but I'm okay with that.
ETA: After reading about some the things you added, I just wanted to say a couple of things myself. 1. Sometimes depression is NOT something you can just "snap out of" - sometimes it's a true chemical imbalance and medication really does wonders, so personally, for what it's worth, I wouldn't be so apt to dismiss it. I don't doubt some of it could be hormonal as well - I get the same way. 2. I know a lot pf people that had babies at 40, and beyond, and while they don't at all regret it, the one thing that they've all said was that they didn't realize how tired they would be at their age, trying to keep up with the little ones. It's one thing to be 33 with a 3 year old, another to be 43. I am going to be 40 next year and again, that's one of the big reasons I am not interested in having another. 3. Like others have said, having issues with depression is not the time to making such huge life-altering decisions like having another baby. And if finances would be that tight, you need to consider what your kids that you have now would possibly go without because there is another sibling to take care.