I am so sorry you went through all that. I would strongly recommend contacting the head of midwifery in a few weeks and asking for a debrief. You need time to process what's happened to you. In the meantime, you need some support - please talk to your health visitor and be honest about everything. Show her this post if you feel you can't talk.
I suffered a third degree tear and had similar issues. Mine was repaired, but the stitches got infected and I ended up healing badly. I had difficulty recognising when I needed to poo, because of the nerve damage, so I never had more than a few seconds warning that I needed to go.
I had lots of treatment in the year after giving birth, which ultimately ended up in a simple operation to refashion the tissue, and everything has been completely fine ever since, almost like I never gave birth at all. The continence issues gradually improved over the year. You WILL heal. It WILL get better.
Can your husband take some more time off? Unpaid, if he has to, if you can manage? If not, don't panic. I remember how overwhelming it was for me, but I got through, and you will too. Your husband needs to understand that this is his time to step up - he must take over everything else, even when he's back in work, so you're only concentrating on looking after yourself and the baby during the day.
I also had to stand for nappy changes, but what made the biggest difference for me was using the changing table we'd bought, but perching on the edge of a breakfast bar stool, so I was standing but also sitting slightly. Can you pick up a cheap stool and try that?
Don't feel pressured into having lots of visitors, but try not to fall into the trap of cutting yourself off either. Be honest with family. Let them visit and support you. Any work colleagues or vague acquaintances who fancy a visit can be put off.
Keep chatting to us on here. It took me a long time to bond with my son, but I did. I never thought I'd have another baby either, but I did! I had a c-section because of what I went through, and that will be an option for you too in the future.
Huge hugs for you. You're doing so well, even if you don't feel it right now. 