How did you know when you were done having children?

Well I am a single mom of 3 boys and all 3 are birth control babies!!! I was positive I was finished as I am barely making ends meet now. Needless to say I am 6 months pregnant! my boyfriend had a vasectomy so I thought I was ok, guess not!!! I seriously thought about not keeping this child because of a finacial and mental point. I did decide to keep the baby and I am soooo glad I did, because it is a girl!!! I know it will be so hard but I believe you can never be finacially ready for a child, so we will see what happens. Oh, I do work full time for the army and have been enlisted for 12years so I do make good money but daycare seems to eat all my money!