What Causes Delay In Periods?

I am on the pill. During my 7 day off I usually get my period on the Wed. This time is hasn't really come. I see a little blood when I pee or wipe. I rolled a peice a toilet paper up and placed it inside and a little bit of fresh blood and brown came out. I am a little stressed at the minute. Could this be the reason? Should I go see a doctor. I'm getting more stressed out thinking about it.