I'm glad you have posted what is happening to you, you are definitely not alone in that factor. I'm sorry about your recent breakup and your current relationship worries. This alone must be taking a toll on you.
Like you, I had postnatal depression as well. It was horrible, difficult for others to understand and made me trapped in my head too. I am too on medication which mostly serves me well, but there are days and months I wonder if I am any better than when I was with postnatal depression. My relationship has suffered terribly and is undergoing another strain with me falling for someone else. (It's definitely one-sided).
I just wanted to let you know there are a lot of us out there. You are not a bad person out there all alone. You are a single mum who needs support and help to get through what you need to at the moment. I get my medication tweaked and checked regularly.
I also wanted to let you know there is a light at the end of the long tunnel. Despite this recent upheaval, (I am seeing a counsellor and my usual GP), I am feeling okay recently.
Take care of yourself and kind Regards