letrozole 7.5mg, did not ovulate, period is late

Nelly
Hi! I'm hoping someone can help.  I have never missed a period, ever.  I took letrozole 5mg for 3 mths and ovulated.  Last mth, my dr gave me letrozole 7.5mg and I did not ovulate.  Now my period is late, 3 days so far.  Took a pregnancy test yesterday and it was negative.  Is this normal since I did not ovulate.  I have always been regular.