Super late and don't know why??

Morgan
I've had super weird periods ever since I delivered my daughter five months ago. The last time I had sex she was five weeks old, and I started two days later and it ended after like...two days. Ever since then they've all been weird, unpredictable and not as painful as normal (not that I'm complaining there lmao). Now I'm six days late. I'm not breastfeeding, I'm formula feeding so that can't be what's throwing it off. I don't know why this is happening! Is this bad? Should I go to the doctor?