Period after labor

How long after labor did your period return?

Our little guy is 9 days old and all my cramping was gone and I had gotten to that really dark/brown end of bleeding. Then today when I walked to pick up my kindergartner I knew something wasn't right. We get home (20-30 minutes total there and back) and I've soaked a daily liner that I only had on because I wasn't positive labor bleeding was over. At first I just assumed it was from the walk but now I'm having light cramping and wondering if it could already be my period?

My last labor was almost 4 years ago, help me remember if this is possible!