when DS was about 4 weeks old, I found myself walking around the neighbourhood with him in a pram, tears absolutely pouring down my face as I thought about all the ways in which having a baby was the worst idea I'd ever had.
In retrospect, there is no doubt I had some PND. And it becomes a bit of a self perpetuating thing because you're so tired and anxious, the smallest thing makes you wake up/disturbs you and then you're even more tired and anxious.
I would second speaking to a GP. They might not do anything in the first instance, but it gets the ball rolling.
I found a babysitter who came and had DS for 4 hours once a week. I didn't do a LOT during that time, but it helped that I wasn't sitting on edge waiting for him to cry.
DH was amazing and your DH needs to step up. He would come home from work immediately and take over for a while. Often he would send off to the big sainsburys as it was the one place I could get a coffee or be inside at that time of night and he would do bed and bath time.
The broken sleep nearly killed me. Again, DH or my mum would have DS until about mightnight/1am while I went to bed early. Then, it had been a bad night (usually it was) anytime DS woke after about 5:30, DH would handle. He'd often bring him downstairs and he'd snooze in his pram while DH snoozed on the couch, or he'd put him in a sling and do some chores. He would keep him until 20 minutes before he left for work at which point he'd b ring me a cup of tea so that I had af ew minutes to wake up before I was back on duty.
Also, my BF told me repeatedly that it starts to get better at 6 weeks. Then again at 12. she was right.
Good luck. It IS hard. You are not a bad mum for feeling this way.