Letrozole HELP!

For the last 3 months I have taken letrozole 5 mg cycle days 3-7. Each month progesterone levels have been indicative of ovulation. One of the assistants at my doctors office today called letting me know I did ovulate again this time. So I'm 12 dpo and am about 98% sure my period is on the way. I can just tell, by the way my body is acting so that being said, I would call my doctor again this Thursday or Friday letting him know yes, I did start so he can order me another prescription to start taking on the 3rd day of my period. Only this time he wants me to take a pregnancy test 6 weeks out from this period. I guess I'm just confused because in that time I would have ovulated from this next round of letrozole and would have another period in that 6 weeks if we don't get pregnant again 🤔. Can anyone explain to me why? I'm just so confused lol I'll do what he says, of course, but theoretically I would be taking that PT around the time I would be ovulating again?