Advice on how to get best results

I'm new to glow and I've never been able to remember what day I started/ended my period. I think I'm close on the Calender but idk. All I know is my last period ended a few days before Thanksgiving and I was on it for 4-5 days. Also on the fertile days the percentage isn't very good? I know I'm very fertile but I recently had my nexplanon removed in august so idk if that decreased my fertility some. I just need someone experienced with this app to tell me how to get the best results and help me understand this app better.