Starting mononessa birth control?

So today I went to my doctor and got birth control. They prescribed it over the phone and told me to read the directions. I’m a little confused on when to take it. The directions say to wait until the first day of your next period or Sunday start. I’m on cycle day 5 (started my period Nov 2nd, done with heavy bleeding but still bleeding a tiny bit). Can I start it tonight? It doesn’t say in the directions but I’d like to if I can