Ortho Tri-cyclen Low, early period?

I've been on birth control for 4-5 months now. My doctor recommended I start on a Tuesday even though I had had my period 2 weeks prior. Anyway, I always get my period 2-3 days early, before I start the placebo. Does this mean the BC is ineffective? What can I do to make sure that my period starts while I'm taking the placebo?