Irregular Period

Cassidy
I started the pill a couple days after Christmas, around the time I was supposed to get my period. I didn't get it until 11 days later, and now my period has been going on for double the time it usually does. 
My periods used to be extremely regular and last 4-5 days, but the pill has messed everything up and I know it's common but I don't know what to do, my intent on going on the pill was to stop my period not for it to prolong it. What should I do?