Postpartum bleeding or period?

I'm currently 5 weeks postpartum. I stopped bleeding around 2 weeks postpartum, started spotting again a couple days later and that lasted until 3 weeks postpartum. I stopped bleeding completely until 2 days ago when I really excercised for the first time since giving birth. I've had brown colored bleeding since then. Has this happened to anyone else? Is it still considered postpartum bleeding or is it my period starting? TIA!