letrozole causing longer luteal phase?

Lou
I am currently about 17dpo. I could be off a bit because I stopped doing LH strips after 2 days in a row of strong positives (I wish I kept checking). I have an average 14 day luteal phase. I have heard that the luteal phase can be longer on letrozole. I did do a hpt yesterday and got a bfn. This is messing with me.