What Causes Light Period?

Hi, I normally have quite a heavy period and this month it s basically non-existent. Its a very light pinky colour and is very light in flow. I normally have to change my pad every 3-4 hours but this month i can wear one all day without changing it. I have had no cramps or any of my normal period symptoms (Headaches, acne etc.) I started it 2 days ago and I think its finished now as I have nothing on my pad after 11 hours, Any idea what this could be?