When to start Femara?

Allie
My husband & I have been TTC for a little over 2 years. My doctor finally prescribed Femara this cycle. She gave detailed directions to start in cycle day 5, and gave days of when ovulation should happen, and when to BD. Well my period hasn't shown up yet. It was due 3/11. I've taken a few pregnancy tests (have felt a little off lately), but those were all negative. 
Yesterday (3/16) my doctor said I don't need to wait for my period to start the Femara. Has anyone else done this? I'm worried that I'll start & AF will show up or I just won't benefit fully from the Femara since I didn't wait for AF.