Letrozole, late period, negative test

Keren

I took letrozole and then had LOTS of intercourse during our fertile period. Then took a blood test which showed that I indeed ovulated this month. Doc said to wait and hope it happened. Now I'm 4 days late and test is negative. How long should I wait to retest? Last time this happened AF didn't show up for weeks and finally I took duphaston to get my menstrual cycle started. Just really bummed. Anyone have this happen to them?