AF late by 16 days now brown discharge... help!

Went to the doctor yesterday did a pee test negative. .. said I have to wait a week to get blood taken.. but last night I had super light pink discharge and now brown... with slight cramping.. sore boobs not when touched just throbbing. .. missed period by 16 days so is this the start of it coming?? Been ttc baby #2 for three months and this have never happened. . Not with our first when ttc and not anywhere in between then!!! Thanks in advance!