The pill

Okay so I had been on the shot for about 9 months and I was on my period the whole time then I got on the pill (while still on my period) and had sex four days after consistently taking the pill. Now it says that if you start the pill on your period you are protected right away but you aren't protected if you don't take it on your period and should not have sex until seven days after. But how do I know that I'm protected since I was on my period that whole time?