I never had cramps until I had kids, now they are pretty strong. I don't know how old you are (getting close to perimenopause?) but chances are there is nothing serious going on. Your body changes considerably after giving birth, especially if you breastfed. That's a lot of hormone changes and cycles can go weird.
If you did go to the doctor, they'd be able to examine you and make sure there's nothing wrong (cysts?) and probably suggest birth control pills to control the cycles better. Might as well go get examined, it'll be a relief to hear from a professional that it's normal.