Discharge

Hii can anybody help me i had sex on the 8th of this month everyday to the  15th my fertile days were 10th - 15th and today i had abit of brown discharge which i have no clue why and i have downloaded some period apps to help me out so i know when im due this one says in 6 days and so does three others i tried but another says in 16 days my period is due and i have been using this one for a while but if three other apps is saying 6 days surely there right? So i dunno if its implantion or what? Helppp please