What Causes Irregular Periods After Giving Birth?

i am 38 years old i have 2 children 18 and 21 after my first child was born i had periods every other month after my second was born af was coming every other month than every 2 months and so on now it can be 7 or 8 months before i get af not to mention after baby 2 was born i had blood clots the size of pop cans dont have that any more just no af for 7 or 8 months at a time went to bathroom tonite lite pink discharge what could be going on