What Causes Delayed Periods And Brown Discharge?

Hello! I ve been keeping track of my period for the last few months and it has a prediction date of when my next period will start. The prediction this month has been for July the 4th. I never got it but earlier today (july the 6th) I had brown discharge but just ever so slightly. So just about three or four drops. I had protect intercourse on may 25th, June 10th and June 25th. I m quite stressed out, I am 18 and my last period was June 4th. Other symptoms are a bad headache. I will be taking a pregnancy test, please help on if you think I am pregnant or if I have baby fever :( thank you so much