What Causes Delayed Periods?

I am almost 2 mths late on the 18th to be exact. A week ago I thought I had gotten my period but no false alarm. 5 days ago I also thought I had gotten my period but no it was only brown and now when I go pee I wipe myself and It is just a light pink I put a pad on and I check in an hour or 2 and it is clean. What can it be either im pregnant or am I just stressed or might there be another problem.