3rd round of Letrazole but opk is negative...

Judith

Hi ladies.... I have a question...I'm not that experienced with opk's.. so far since I started Letrazole 2.5mg every month usually CD13 or 14 I get a positive opk. I started 5mg this mth and I am on my fertile week.. I have been checking all week and all my opks are negative...according to my calenders I ovulated yesterday. I am using clinical guards and dont know if they are reliable or if this round failed to make me ovulate😔... please help!!!