When should I start Provera on my 2nd cycle?

Cassie • I am 1 in 10- PCOS fighter.
My doctor prescribed me Provera for 3 months. I took it for 10 days and got my period April 5th-8th. She wants me to take it for 3 months. Should I start it 10 days before my period is due? Or wait until my period is late before taking it? I never get my period when I'm not on bcp