Question about birth control and early periods?

I've been on birth control for 4 years now. I switched last year from the patch back to the pill. I had some problems with breakthrough bleeding with the first type of pill my doctor prescribed, so in December, he swtiched me to another kind(TriNessa) I haven't had any breakthrough bleeding with this pill until now. I am on my last week of active pills and I've started my period! Is it possible to have breakthrough bleeding after being on this pill with no problems for 5 months? I haven't missed a pill at all this month and I just don't get it. Am I going to have to change pills again?