I am sorry you are going through this, I am not an expert but I didnt want to read your post without comenting.
Being a new mum is hard, I remember it well feeling isolated and lonely and not really having the first idea what I was doing. But I am sure you are doing fine, and no one can be a perfect parent.
Its a shame but babies don't come with an instruction manual, and it can be very difficult at first.
If your baby is happy, smiley eating and sleeping as he should be, and is growing, I think that that counts as a sucess.
I think you should also consider seeing your GP about your depression, its an illness like any other, and it sounds like to you need the support. Have you got a Health visitor you can contact if you are worried?
Popping along to a mother and baby group if there is one in your area might be good for you and your baby. Its a hard job on your own, and maybe some other mums could be supportive to you.