Yes, that is the experience of my sister (who has five children) and a good friend (who has six).
It's definitely my experience too.
6 kids and pregnant with my 7th.
I have become disillusioned about NFP and am seriously considering a tubal ligation after this baby is born.
I have many health problems and am exhausted and cranky.
I'm having a hard time believing it is the will of God to have more kids than we can care for.