Quoting Ivana*mommy of two*:" Hey Mamas!! My son is 21 months old and still nursing frequently! My first post partum AF is still nowhere ... [snip!] ... will not let him nurse at all except twice a day, one for his nap, one for his to fall asleep at night, and that will be that."
Sorry you're having a tough time with it. I agree with the others who talked about setting boundaries.
I got my period back at 23 months and I know exactly why. My husband and I spent our first night away from our children (both nurse frequently, the almost two year old nursed about 3 times a night), we were gone for 24 hours, I pumped twice, just for a few minutes on each breast. 5 days later, I ovulated (I actually felt ovulation pains for the first time in my life), 14 days later I had my first period. I had heard that spending some time away or quickly weaning can bring back fertility quicker.
Also, nursing at night helps your period away longer.
I know you are frustrated, but quickly weaning, especially if your son isn't ready will be difficult on both of you (both emotionally and physically). Try to drop nursing sessions slowly to reduce your chance of clogged ducts.
Have you read Mothering Your Nursing Toddler? It has some wonderful advice on how to deal with how you are feeling. If you are considering nursing longer (not trying to pressure you into it), then it is worth a read.
Best of luck
Oh, I'm currently nursing two children who have past their 2nd birthdays (one just turned 4), I didn't expect to be taking this adventure, it just didn't occur to me). For the most part, I love it but I sometimes feel manipulated by the 2 year old too. It usually happens when I feel like I should be doing other things, but then I realize how real his need is and how he will only be young for a short period of time. I do miss sleep though (he nurses frequently through the night and we haven't had luck gently weaning him at night since we had a death in the family a few months ago).