When During The Cycle Is Right Time To Check The Ovulation?

Hi i am trying to get pregnant so i am checking my dates all the time and using my ovulation machine for testing i was into my 17th day still testing and had some spoting it was dark brown i was told this could be 1st sign of pregnancy mmm i thought but then 2days later i had a really bad period im always 28days !! now i dont know when to start ovulation testing again please advise