Messupmum - first of all, you're not a mess up Mum at all. You are a woman who is suffering from a mental illness that is surrounded by a world who alternate between caring and not caring. I can tell you categorically that you are cared for - if only by strangers on the internet and especially from someone who suffers from anxiety and BPD (me).
I don't have much experience of the severe depression that sounds very painful so I am not going to pretend I know how it feels. My BPD means that I do have moments of this, but they are infrequent.
Medication isn't always the way forward with BPD, but if it is the depression/anxiety that is propelling things at the moment, it is better to address them with medication.
As for the CPN - if you feel you are not getting adequate support it is in your best interests to get someone who will be able to support you better. Also, it helped me to have a collection of "safe" people - that means that when the sh*t hits the fan (which it does for me, often), I can call them up without the fear of judgement. I only have two safe people, but it is better than none. Doesn't matter whether the safe person is a long term friend or someone you met last week - whoever you feel you can be genuine with. If that is on MN, then you do whatever works for you.
Small, achievable goals are the way forward. Do not think about work. Think about each day as it comes. Today is not such a good day - retreating to bed makes you feel comfortable - fine, do it. It may feel demoralising, but ultimately you have to do what YOU need to do to feel SAFE.
I found routine absolutely key in getting better (although I'm not better as such, just a bit better than earlier in the year) - but make sure it doesn't become a pressure cooker. Be realistic about what you want to do and what you can do. If it's not a lot - that's absolutely FINE.
As for the bad days - I had one at the weekend. I was all ready to just jump on the first train out of sh*tsville and run some kind of cult. But I tried very hard to remember that in spite of the crap day, I have had some good days recently. Although the bad days seem endless and crushing, there are good days.
Two quick things. I would look to see if there are any psychotherapists that would be willing to come to your house on a week on, week off basis. Meaning that one week they come to your house, and the next meeting you try and get out of the house, even if it's to a local park over the road. I don't know where you are located, but a few in my area did that.
Lastly - this helps me each day;
Do 1 thing you have to do (washing up, writing an email, etc)
Do 1 thing you WANT to do (have a nice cup of tea with a biscuit etc)
Do 1 thing that will make YOU happy (listening to a good uplifting song, watching a film, cuddling in bed - anything).
I hope that helps, and sorry for the essay!