clomid cd 5-9 vs 3-7. only have a 3 day period

Madi
Ok so I've done two rounds of clomid so far. My doc told me to take it cd 5-9 but my periods are only 3 days long so I'm always done with my period before I start the clomid. I have been reading a lot of people saying you should start it while still on your period, is this true? Should I try taking it cd 3-7 instead?