Ladies, I have a question!?

How long does breakthrough bleeding last? (Sudden spotting), I've been on Loesterin24FE for since 03/20/09- untill now, I haven't missed a day. I had my period on 5/21/09 for 4 day's and finished but recently i started having bleeding since monday so basically 4 day's already, it feels like a period with lower back pack pain, and cramps... it goes away by night time but it comes back in the morning. It's a very light flow. has anyone experience this before?