Help,18 days passed period now noticing dark brown blood

Kayla • Ttc baby #1👶🏻 with Pcos.

I took a test tonight and it was negative, took a nap cuz I was exhausted I mean like a 3 hour nap, woke up and notice dark brown like blood should I assume this it just a period its nothing like normal dry/ dark blood I get after a period.should I assume my period will start now and stop taking tests or should I keep taking them??