I think it's beyond difficult when you have one DC, to realistically visualise life with additional children in the long term. My first pregnancy was an absolute joy, if I was tired, I could put my feet up and rest and sleep in the afternoon if I wanted to.
When DC1 was born, I was a SAHM, so if we'd had a really awful night, we could sleep in, if I was shattered, I could sleep when DC1 slept. There was no one else to factor in, so life was pretty easy and could roll at DC1's pace when it needed to.
I found motherhood with 1 DC a pretty chilled out place.
All of that can go out the window with DC2. When you've had no sleep, but still need to get up and get DC1 to nursery/school, or when one is ill and you're up all night looking after them.
If you opt for a 2nd pregnancy, you won't be able to sit with your feet up & sleep when you're shattered, unless someone else steps in to help, the same when DC2 is born.
If you found preganancy 1 easy, tbh, it's probably because you didn't have any other DCs to take care of at that time.
Being pregnant when you already have another child is completely different IMHO.
If I hadn't been in the position of having additional DCs after DC1, my concept of pregnancy would be what yours currently is, because that would be my reference point. The tiredness came as a shock, but tbf, when DC2 came along, I already had one child at school with various hobbies (biger age gap than you would have).
Even so, you can't over estimate how much harder and more tiring, even in good health, being pregnant and having a newborn is 2nd time around.
Surely, though, the main crux is, that your DH isn't ready for another child, so to press on with this, given your health issues doesn't even seem like an option to me.