I have 3 children and we always planned to have 4.
We started trying for No 4 and after 18 months of nothing, we decided that we didn't want to carry on trying indefinately and that it was "natures" way of telling 3 was enough. As I had the 3 close together, I didn't want to have No 4 a lot later on so it ended up being on its own.
Anyway, life got a lot easier - I had gone back to work part-time to a job that I love etc etc.
Then in December, I had a "scare" and I was horrified to find myself feeling absolutely "gutted". I spent a whole week crying my heart out and praying that I wasn't pregnant, even though financially we could afford a 4th and we had a big enough house etc.
That was a real "wake-up call" to me - and we both realised that we were blessed with 3 beautiful healthy children and life was perfect.
So 3 weeks ago, DH had a vasectomy - and although friends told me I would feel sad - all I felt was a huge wave of relief.
I always said to friends "how do you know when your family is complete?" - but when it's right, you just do, it's really difficult to explain.
Good luck anyway.