Letrozole tablet. Letrozole tablet?

Hi, I got married before 6 months back, had a prblm like irregular periods but for the last three months am getting regular menstrual cycle.. Gynaecologist gave me overall pills for 1 month..After consuming that tablet am getting regular periods consecutively till date.. Now the prblm is like after taking overall, doctor gave me letrozole tablet to be taken on 2 to 6th day to get pregnant and doctor told the relationship days too be had. Last two months I took letrozole pills, but I don't found a chance of getting pregnant.Gynaecologist told to take one more month letrozole pills. So my question ,Is letrozole is harmful for the body? Why as of now am not conceived though my menstrual cycle occurs as normally, after taking letrozole tablet? Can anyone gynaecologist in this forum please help me out on this ...