Period while pumping?

Al

I was told as long as I was pumping/breast feeding I would most likely not have my period. I'm 2mpp and I stopped my post partum bleeding about 3 weeks ago. Last night I started spotting lightly mostly brown blood. No cramping and it hasn't increased. Is this normal? Has anyone had this happen and how long does it last or does it end up turning into a full blown period? I'm not on any type of birth control.