Period while on BC

Olivia
so I just recently started BC. I'm on the last week of my first month, and it's the dummy pills. However, my period is how it's always been, maybe just barely lighter. But I have a heavy period. I don't know how BC works usually, since I'm new. Am I supposed to be having a regular period or just light spotting and bleeding? 
Also, does it take 2 weeks for BC to become effective?