Bleeding for really long?

Vivian
So usually my period is quite short- around 5 days. I take the pill continuously (3 months, then a break and so on) and I had my last period in October. Around the 12 of Jan I started bleeding while on the pill! Does anyone know why this might happen? 
I stopped taking the pill on Thursday and started re-taking today. If I continue taking it, it will definitely stop, right?