5 months pp

So I'm 5 months postpartum and I exclusively breastfeed. I've gotten my period regularly since giving birth while breastfeeding. this month for some reason has been different. I've only had pink and brown spotting. I've been nauseous throughout the day. those that are exclusively breastfeeding and have had their periods regularly have you experienced something like this before? I'm just wondering if my hormones is just causing me to spot. if spotting doesn't count as a period, I would be 4 days late.