I'm just wondering,

Last month my bf and i had some unprotected sex but my period for that month came so i didn't bother with a PT.
This month however we did absolutely nothing at all (because I was overseas) but now my period is rather late (by 5 days) and this morning I had a brown discharge.
I have been on and off in stress for the last few weeks, but I never missed my period due to stress before, neither do I have irregular period or missed period before. Recently I was sick and did some really heavy exercise.

So are those the reason for my late period? I mean, I can't be pregnant, right?