I probably shouldn't be commenting here because I only have the one. (We wanted more but wasn't medically possible.)
Also, I never really wanted "children" in abstract but I did very much want my husband's children.
Anyway op, the answer imho to ">why do we do it to ourselves?" in a nutshell, it boils down to LOVE.
Yes, you hear about all the difficulties and challenges on here and they should not be underestimated - but one doesn't hear as much about the positive side - because it is unfathomable/difficult to describe/impenetrable - but no less powerful for that.
For me, the entire world "clicked" once I had had a child. It's a constant challenge, you are no longer in control as you once were, it is the oft-spoken about roller-coaster, and emotionally draining x 1000, but parenting challenges you to learn a lot about life and learn a lot about yourself and takes you down many unexpected avenues.
Above all that is the fact that you and the person you love most in the world have created a complete, unique, individual human being, for whom you would gladly and without thought or hesitation throw yourself under a bus!
That's not a small thing.
It's utterly life-changing. It can be at the same time utterly wonderful and utterly dreadful all bundled up in the same moment. But above all, imho, it is a blessing and a privilege.
Having said all that, whether I would be saying the same thing if I had five dc I don't know!
But I came from a large family and feel that all the things a family (ideally!!) provides such as love, warmth, stability, selflessness, etc etc are all ultimately worth so much more than money, lie-ins, a wobbly stomach etc etc. Easy for me to say perhaps when I do get the odd lie-in though I suppose!
These are just my own personal opinions however. Each to their own! I just wanted to put the counter argument because you (understandably) hear so much about the other side on here (it being a parenting support site).
I hope things work out for you op whatever you decide 