Honey, even when you've got an easy baby, you shouldn't have to be alone. It's just not the way nature intended motherhood to be. If family cannot step in, hire as much help as you and DH can afford, maybe not to look after the baby, but to cook and clean. My DH works really long hours too and can only help a little bit w/the kids, and I know what it feels like.
Also, everyone's depression, although on the surface may look the same, and we have these labels like PPD, everyone's cure will be different. Medicine/and or supplements can be part of the mix, but there are also other things you can do.
PM anytime if you need a little pep talk.
I used to be a shopaholic, now I'm a create-a-colic! (Mother to two boys)