What Causes Spotting?

i usually have a 7 day period and the first 3 to 4 days are kinda heavy. its always on time ans lasts exactly 7days. last month i was 4 days late but it was 7days. this month i was on time but on the second day i was begging to spot, the last 4 days was just pinkish orangish spotting. what does that mean