It's possible to get false negatives until the HCG hormone is at a high enough level in the sample (preg tests work by measuring this hormone)... Anyhow, long story short, test at 10-12 days after ovulation, like the first day of missed period would be good... And test with first urine in the morning (waiting to pee all night, the hormone is strongest w/ first pee of the morning)... and FYI the Dollar Tree preg tests are the same as the $15 clear blue easy type tests.. Equate tests from Walmart are not very good to use for early detection... It all depends on how sensitive the test is to checking for that HCG hormone. but the Dollar tree ones are good for early detection. And how do I know? Personal experience! My husband and I wanted to be preg and I tested like everyday (that can be expensive... that's how I discovered the $1 Tree ones)...
Good Luck!