he will be picking up on your stresses, which will make him stressed.
He is pobably going through a clingy stage... just try to say to yourself, he is only a baby and when mummy leaves the room, he isn't convinced you will come back. Agree it is stress full!
Do you get out of the house much? if your baby can sit up, you could sit him in the baby swings at the park, and get chatting to other mums?
It sounds like qa lot of your problem is isolation, and I would feel miserable too if I was isolated.
If you ever feel like screaming at him, or hurting him, go and put him in his cot with some safe toys, and go downstairs until you feel 'safe' to be with him.
Mumsnet is good for chatting and support, where do you live? You could join one of the meet up threads, would get you out and about with some adults. Or the post natal groups?
Hope that helps, and hope you feel better soon. If you feel that things couldn't be remedied by a better quality of life for you, maybe you should go to your dr and ask about some anti depressants, as PND is a truly evil illness, just as flu is an illness, and your dr can help you.