we are in the exact same boat! except my son is 22 months. i really started getting the itch at about 18 months; i can totally relate to watching everyone else get pregnant, and just wanting to have some control over things! We also eat a more traditional diet, and if you look back at more traditional cultures, child spacing was much further apart than it is nowadays.
i have started to try to stretch out the time between nursing sessions...i find some activity to distract him when i know that it's coming up on a time ds usually nurses at. and i will try to offer him a snack instead while we are out. it typically works, however if we are at home, he will rather nurse than anything else. DS is similar, where he doesn't eat a lot of food... he would rather just nurse, and he will ask every one to two hours while we are at home. i am getting a bit touched out! since i have introduced my distraction technique, he does nurse slightly less, in general. And he eats a bit more than he did a few months ago, for sure...just still not as much as other kids his age might...although, i have an idea that since we eat so many dense foods, he just may need less. and i think it's totally normal for kids to eat their fill of one food one day, and then not again for a while. i was surprised that my son really likes sour foods. and he is a big meat guy...he loves the stew i just made. but he won't eat fruit at all, ever. and he will only eat veggies in stews. or if i hide them in a muffin, but even then, he will only eat a small amount of it, so i think he just doesn't NEED those nutrients. and once he started eating more, he also started sleeping better...that may be a coincidence though. as soon as he started sleeping better, i got some good fertility signs...and then we got colds, and he's nursing all the time again so i really do think that having a long stretch without nursing is a big contender in terms of getting fertility back.
you do hear that some people don't see AF until after full weaning though....and i can't help but think "but that's so unfair! i don't want to wait that long!" ...but we shall see. i have faith that our little nursing dyad knows best, even if i don't see it now.