Clomid 3-7 vs 5-9

Tiffany

Hello! I did my first round of clomid this month days 5-9 and unfortunately starting spotting today so I’m considering my self out. The doctor gave me a refill and was told to do it cd 5-9 again. Just out of curiosity why do some people do cd 3-7 and some do 5-9? Is there a difference or a reason why?