I was in the exact same situation as you after my 3rd.. I had never had that incredible urge to have babies but after my 3rd I just wanted one more.. I used to get teary and Dh was adamant he didn't want a 4th.. When our Ds3 was 8 months old we had an almost oopsy.. We thought I was but i wasn't. It got Dh thinking and here we are now with our 4th..

maybe because your 2nd is still so young.. if you sit your Dh down and talk about why you have these urges and if you can both list positives and negative for having a 3rd.. I told my Dh that it wasn't fair we stopped just because he wanted to and it needed to be a joint decision.. I said that I felt if we didnt have a 4th i might resent him for that and he in turn said the same thing.. It was a big decision to make.. we pretty much talked and talked for 8 months. then we came to a solution.. We gave ourselves one year to fall pregnant. so I had till July 07 and one of us was to get "fixed" I fell pregnant in the April and I had my tubes tied..

I am not sure if that helped.. but was just sharing my experience