Ovidrel shot 3 weeks ago..help?!!

Estefani
It's been 3 weeks and 5 days since my Ovidrel shot after taking Letrozole but still no period...took a test and it's negative...any opinions? 
-First time taking Ovidrel
-Since I started this process back in August I get my period after 3 weeks and 5 days of taking Letrozole