I'm so sorry. I've been where you are, and it is devastating. You are in the worst part of it right now, and unfortunately that is something that you do need to go through, but you will come out the other side. Your unhappiness is caused by the great love you have for your baby, and it honours him, even though it is so very hard for you.
The best advice I was given at the time is not to try to deal with this all right now. Little by little, you will feel more able to cope with day to day life, and the physical pain of it will ease. It took me about 2 years to feel "normal" again, but it did happen.
Concentrate on the small things that mark the stages of each day. Make sure you get up and get dressed. Make and eat food. Leave the house (even just to empty the bins).Talk to another adult if you can manage it. Individually these things are tiny, but they will give you a framework to cling to.
As time goes on, make a small plan for each day (bake a cake, buy a newspaper, walk the dog, anything really). Try to feel the achievement that doing these things represents. I changed the place I did my shopping, to avoid seeing people who might ask for news of my baby (this happened once, and I had to just leave my trolley and run out of the shop).
I would be cautious about forums like SANDS- I was looking for some hope and for someone to tell me how to get through it alive, but I found the forums actively unhelpful with that- I may have tried at a bad time, or the people there who were the most negative may have left, but it isn't always helpful. I was a member of a feminist board at the time, which was much better for me and really helped, because there wasn't quite the same danger of being caught up in hopelessness.
The flashbacks are hard, I was tormented by them. A psychologist friend told me that the best thing is not to fight them. I found that they eased off a lot as soon as I just accepted that they were a normal part of the process. If you feel that you need someone to step in and help, then speak to your midwife or GP. My midwife visited for a month afterwards and although she was lovely, I found the weekly visits really set me back and I asked her to stop. I'd be just about coping and getting through the week and then the MW would arrive and I was back in the middle of it again.
Once again, I am so sorry that you are going through this, but I hope this thread has helped you to feel less alone.