Well with dd1 and dd2 I only fed for about 3 weeks and by 6 weeks weeks I was on the pill so cant help there....
with dd3 I full time expressed until 8 weeks, then formula fed with the occassion... lets see if she will do it.... and now shes 16 weeks and still no af. I havent gone back on the pill to see what my body does and if we do decided to go again.... yeah! I dont know if that answers anything but I think your body is probably different every time....