My doc just prescribed clomid (clomiphene) for cycle days 3-7 but my friend also on clomid (clomiphene) says she takes hers days 5-9 what is the difference? i have pcos

No big difference: Studies show pregnancy rates are identical starting cc on cd 1, 2, 3, 4, or 5. The main difference is starting later its less likely to have a persistent cyst from the past cycle. For patients not monitored by ultrasound cd 5 may be a better choice, with monitoring it makes little-to- no difference.

None: It does not make any real difference which regimen you use, the result is the same. There is a greater chance for ovulating after taking the Clomid (clomiphene) either way.