I have been lurking a little - too busy for MN these days, but I just wanted to say it is good to know I'm not alone in this!
I have a senior role in a demanding industry, I joined the company when my youngest was just over 4 months old. He's now 9 months, and I also have a DD (8) and a DS (10). On top of that I am a single parent, and basically just find everything too much. My job is killing me, I am quite a perfectionist and am being forced to settle for far less than perfect due to internal politics, and on top there is just so so so much that needs fixing. Basic set hours are 40 a week, but I now work through all my lunches, come in early and leave late where childcare permits, and usually have to work at least a day each weekend just to keep my head above water.
I spent most of the bank holiday cleaning my house because I don't have time for it usually (not an excuse for general laziness, I really don't, because I collect the children, then it's bath time, bedtime, a little play time if I'm early enough, then typically I catch up on the lap top with work then crash out)
I think I have had enough. I cut my arm pretty badly a week ago because I just needed a release. I steri stripped it up myself but it was v deep. I also overdosed a few months ago. It makes me so cross with myself that I am totally failing my kids by being so damn selfish as to do that and potentially damage them. And I see so much of me in the older two as well. But then I get feeling so bad I reckon they would be better off without my influence in their lives 
I saw my GP a few months ago who diagnosed PND and who won't prescribe meds because I am still breastfeeding, and wanted to sign me off, but I cannot afford to be off work. And I won't stop breastfeeding - it is the one thing that makes me feel like a "proper mum" to my baby.
Sorry to just appear and rattle on. I can't tell anyone what things really feel like.