What Can Be The Reason For Spotting Continuously?

Hi, i am on the pill (Yasmin) and have been on it for the last 3 years continuously. After missing 2 pills in a row i got a period (which was heavier than usual) and lasted for 5 days. I was still mid pack. This cleared up and on Thursday last week, all was fine. Then on friday the bleeding started again. Saturday was fine, Sunday, there was light spotting and today it has re-started. I am really worried as i am still on the same pack of pills and so i dont think this should be happening.