Clomid 5-9

🌸Grace🌸
I was told to take Clomid 5-9. Last Sunday, around 5-ish PM, I start spotting until I went to bed. Monday, became period and it was Heavy. Tuesday, Heavy period still. Wednesday (Today) period was light, not medium but "light" and Tomorrow (Thurs) I have a feeling it'll be my last day of period. Last month, my period was only 4 days. 
My questions is, do I count Sunday as First Day of my period and take Clomid tomorrow (5th Day) or start counting Monday when aunty Flo was full blown and take clomid Friday? I really need some advice ladies. Thank you!