Confused. Late period.

Samie

I’m 5 months postpartum but I’ve already had two periods around the same time of the month. So if I go off those two I had then I am around 4-5 days late on my period and I took a test last night and a couple days before and they were both negative. Today I went to the bathroom and I had some light pink/brown discharge. Is that implantation bleeding or my period starting? Should I wait a few more days before testing again?