Do you need a period before clomid cycle?

Meg
Going for a scan today to see if I have a cyst and I read if you don't you can try clomid for pcos and TTC but I was wondering do you have to have a period before a cycle of clomid as my period hasn't shown it's a month late and I was going to ask for clomid if all is fine. 
Thankyou. 

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