Was on Letrozole for 6 months now off and a week late period help!?

Lo

I was on Letrozole for six months I stopped taking it and when I did I had a normal period. But this month my period is a week late! I have been tracking my cycle since November 2017 and my average cycle is 27 days. I am so confused could it be from the letrozole or the trigger shot? And yes I have taking 7 pregnancy test all negative.