Very long period

I'm 21, and I've been on Yasmin for the last 4 months. I started to come off for a week like normal, and changed my mind. I only missed one. Everything was fine until a few days after, when I had what I thought was light spotting. It's now been just over two weeks and it's not stopped. It's been like a normal period at points, and whenever I think it's done, it comes back. Is this normal considering, or should I be worried? Thanks.