Should Diane 35 Be Started Now Or When The Period Begins?

I have endometriosis and my doctor prescribed me diane 35 after I had previously been on yasmin. Its been a few weeks since I've taken a birth control pill, I'm now in the middle of my cycle - is it ok to start the diane 35 now or should I wait until my period starts? I'm apprehensive to start my period without the aid of the birth control pill since the pain is normally very extreme. Thank You, Celeste