help ? please....

app says im 18 days late . idk if its true if i didnt ovulate the beginning of the month like it says and ovulated towards the end. but last tues went to the dr did a pee test came negative. still no period . should I test again? how long do i have to hold my pee in before i can test.. ? my bf will be home around 530 and when i test he likes to be in there with me.