Probably be a good idea to start temping, you may be Oing earlier or later than you think and that is why you are not falling pg. I do think it is a bit concerning that you wern't on any contraception for 12 mths and even though you wern't really ttc you didn't fall pg sooner- you may be having anovulatory cycles (where you don't release an egg) and just happened to 'catch' it the right time and fell pg with your DS. GL