Not crazy at all! Up until this pregnancy, I always used to plan the next child whilst I was still pregnant - we actually started TTC #2 when DS1 was only 2weeks old - now that's crazy!!!! LOL
I would have an idea of when I wanted the next baby to come along (roughly speaking) by now if we weren't done this time around... But for the first time ever I honestly don't want anymore and my health can't take it anyway, so there's just no desire. Instead I'm beginning to plan what I'll do with my 6 children over the next few years before they're all away in school fulltime, and what I'll do with myself once they are all in school and thinking a lot about the future...
You're definately not alone though!