What Causes Delayed Periods Along With Pink Vaginal Discharge?

My period is 17 days late. The only time I was ever late was the one time I was pregnant. I've had all signs but negative pregnancy test. I've cramped on and off for three weeks. Today I have started spotting only when I go potty and it's light pink. It has now turned a purplish color but not think and heavy like my normal periods. What could this be?