Postpartum cycle or implantation bleeding? Only lasted one day and was super light

So I’m ebf currently and have started to get what I thought was my first postpartum period. However, it only lasted a day and only filled one panty liner. We are “trying” for another without a timeline, but I didn’t have implantation bleeding with my first so I don’t know the difference between a period and implantation bleeding. So far all tests have been negative. Any thoughts?