Ttc w/ femara

I am suppose to be taking Femara when I start my period. I have always had irregular periods. How do I tell when day one is of my period to know when to start taking femara??? I spotted a little yesterday (light pink) but today it's more of a darker pink/red and its a little more than yesterday but not enough to use a pad or tampon... I've been using a panty liner and its been good enough.... Just curious it's my first time with fertility drugs.... Any advice helps