Femara (letrozole) cd 3-7 vs 5-9

I'm new to glow and very excited to have a community of women that are ttc with me. Here is a bit of history. In 2011 I had a dermoid cyst removed from my left ovary the size of a softball. They didn't remove my ovary. I was also diagnosed with PCOS and insulin resistance. I started trying to conceive in 2010 with clomid and HCG trigger shots with no luck. After my surgery I stopped TTC. Last month I started trying again and my doctor prescribed me Femara 2.5 I have completed my first round of femara and I have gotten a BFN. I am now on cd1 and I will be starting round 2. My question is what is the difference between cd 3-7 and 5-9? When my doctor prescribed  it he said to take them days 5-9. The more I read up on them I'm seeing that more people do cd 3-7. I would also like to know is it normal that he prescribed so many? They came in a quantity of 30 but he also gave me 2 refills. Is that normal amount to prescribe? I would also like to hear some success stories on femara I'm not doing and trigger shots or anything. Just femara.