Hello bigbrother,
I read and posted on your AIBU last night and came back this morning to read this thread, having thought about you a bit more.
Tbh, I'm not sure that the antenatal group (which your AIBU was about) is really the problem or the solution.
To me, based on having read your posts, the theme which does seem to link the different points you make, is that you are not feeling happy and not feeling like you are coping. I'm no expert, but having been diagnosed with antenatal depression myself, I recognise some of the signs of depression in you.
For example, I, like you, started to worry alot about how others perceived me... e.g. you say 'I feel as though they all ridicule and deride me as a lazy, needy, antisocial whatever'. That kind of social fear is horrible to live with and it drags your self esteem even lower. It seems you're almost looking for rejection from your antenatal group because it will prove you right.
I, like you, have also been feeling very lonely (often more lonely when I am with others and feel left out than when I am actually alone).
I really think that you should ask for help - as loudly and persistently as you need to in order to ensure you get it. I realise that this is a hard thing to do when you're feeling low, BUT, having been low myself, found the courage to ask for help and been referred to a clinical psycologist, my experience is that this is a very positive step forward. The psycologist helped me a great deal to understand WHY I feel the way I do. Sometimes that reassurance that you needn't feel guilty or suffer is a huge help on its own.
So, in summary, I think you should start by going back to your GP (with your DH to stick up for you if needed - sounds like he is a star), and pushing to get some counselling or appropriate treatment for your low feelings (I hesitate to say depression because I'm not qualified to make a diagnosis!).
I am lucky that I don't have your health problems, so I don't know much about Sure Start / Home Start, but it sounds from other posters like they are really there to help with your more practical needs. Maybe you should ask for / accept their help too, when you need it, with getting out and about.
MN often looks down on giving 'hugs', but I am sending you one anyway, because it sounds like you really need one.
Stay on here and I'll look out for your posts.