Just how I felt... and I only had one to think of!
But I felt like I was doing everything wrong. Kept shouting at DH. Wanted to run out of the door and not return countless times (although would never have done it... but it was that feeling of totally being trapped in a situation that felt unbearable and un-ending).
Basically, the doc said if you feel happy at the times when you would normally feel happy (like when DD1 would make you giggle, or you listen to something funny, or you see the sun has come out today for the first time in ages... you know... whatever), then it's not PND.
But whether or not it is or it isn't, really don't feel afraid to go and talk to someone (although not if that just adds yet another stress to your day: having to fit an appointment in).
As far as I can tell, everyone feels inadequate and everyone feels like shit for a while.
Do you have anyone nearby who can give you a break? Is DD2's dad around much?
If you are successfully keeping 2 young DDs alive and well in any shape or form, you are not a disaster, you are succeeding! Give yourself a pat on the back and be proud of what you are doing