OMG - what a terrible time you have had - it's small wonder you are now feeling overwhelmed. I take it you have 2 sons as you mentioned undiagnosed OCD after birth of first son. How old is the older one - asssume he was c/minded or day care while you were working. Were you worried you were likely to miscarry at the end of the first trimester, as you say in your post "Had been told I was miscarriage" - and you say this was the start of all the trouble. If I have understood you right you worked 4 weeks of the time when you were officially on maternity leave, and presumably only got paid whatever you got on maternity leave.
It sounds like you are an external examiner or moderator of some kind? YOur manager sounds like one of the most insensitive person to say the least and at worst a bully, as she was sending you to a school miles away when she knew you were having a hard time with your pregnancy. It probably would have been better to talk to your manager at the time when you were falling way behind and knew you could not carry on, but I guess you might have
been feeling a bit vulnerable about a meeting with her, given her attitude.
I must take issue with you about your comment "I totally screwed it up" NO you didn't - you were/are quite seriously ill with OCD and depression. It was you manager's responsibility to be aware of your problems and if she thought you were not up to the job because of your mental health problems, she should have ensured you went off sick, instead of which she piled more and more on you. She is the one at fault over this - not you. I was a team manager for 15 years in social services (retired now) and I noticed that one of my team was not performing as she usually did, so we had a chat and she admitted she was having long bouts of crying, so I insisted she went to the GP and went off sick. It did of course help that I had had depression too but that's another story.
I can realy identify with you when you say how you loved the job and how highly you were regarded (same here) but when mental illness descends we can't carry on like it isn't happening. It's like planning a hill climb with a broken leg.
You are working so hard with the therapy and you have been feeling better but the work stuff is screwing you up. You want to be the best mum you can be - of course you do, but you can't do all these things without feeling overwhelmed - it's called being human! I think you need to break things down into bite size chunks. When does your maternity leave end - is it possible to manage on your DH's wage - is he supportive btw? If it is then you could give in your notice. I know jobs are hard to find, but the fact is you are not in a position at the moment because of your mental health issues to actually be working in any job.
I'm so glad you got the tongue tied thing sorted. This happened to my friend's daughter recently. It was her second child and she knew he wasn't breast feeding properly as it was different from the first time, but he was putting on weight. She was sure he was tongue tied and she asked midwives and HVs and all said "No he's not - he wouldn't be putting on weight if he was" - in the end she insisted she was referred to a consultant paediatrician and he saw immediately that he was tongue tied, and now the baby has to learn how to suckle. Sounds like your CPN was trying to cover her tracks when it was found that your baby was tongue tied and it was nothing to do with your OCD. Why can't these people just say "sorry I got it wrong"
Re this coming meeting. How do you get on with the psych - or have you not seen him/her before. Think you will find the CPN will want to demonstrate to the psych that she is empathetic and sensitive and will be falling over herself to do this. You could I suppose contact her again and apologise for blowing up ather and she should understand that it is perfectly normal to "lose it" sometimes when you are overwhelmed with worries. I think you need to do whatever you feel best about the meeting at the end of month. If you feel you could face it better if you spoke to the CPN then it's probably best to conatct her. If not, go to the meeting with some clear idea of what you want to get out of it. Take notes to remind you if necessary. You sound like you are quite assertive, and that's fine, but try to keep calm and make sure the discussion addresses your issues.
Phew .............take one step at a time ..........can you stop worrying about work, because i think that would help.
Oh yes these email and facebook messages about lost portfolios. Who e mailed you and FB FGS,.....you don't send messages like this on FB. If it was your manager, this is unbelievable. It is highly unprofessional in my view ro be communicating by e mail and FB about such matters. You may be better off out of that job.
Take care and come back and talk if it helps.