No-one is going to judge you, because this isn't your fault! you aren't behaving this way by choice, and it doesn't make you less of a mum. I think you probably do have PND, that sounds exactly how I felt a few months back, down to teh comfort eating, the wanting to be left alone, to have all pressure removed.
Firstly, to echo Dumbledore, go to your GP and tell them how you're feeling. They won't be surprised or judgemental, this is SO common. I was given a fairly low dose of antidepressant and it's helped me cope immensely.
Secondly, can I reccommend Homestart? I asked for their help when I was feeling like we weren't getting out enough, I never got any time alone, didn't have any real friends etc. My homestart volunteer has been fantastic. She will look after ds while I shower, get a bit of space, do a bit of housework etc. Or just talk if I need to talk. It's such a huge help, and she's become a firm friend.
Thirdly, don't assume those friends will be horrified if you admit how you're feeling. Friendships are often formed fastest when you show "weakness" iyswim. If your friendships with other mums at playgroup are just based on how wonderful motherhood is, it will remain so. You need support. The other mums will be there because they need some space too! they may have left a messy house behind, or be tearing their hair out quietly over their babies. It often isn't anything like it seems.
Lastly, your dh telling you to pull yourself together is completely unhelpful. What he needs to do is take the kids off your hands for an hour now and then. Take them to the park, or let you go shopping for a bit. Let me know, as in expressly tell him (cos they can be a bit thick) what he can do to help you. And get a leaflet on PND, or take him with you to the docs so he knows it's not just you and you can't just pull yourself together ffs.
You will get better. The way you're feeling is not permanent. You just need to ask for help and you'll get it.