so confused. (+) and (-) tests

I'm two weeks late for my period which is always on time. I took two test originally 4 days late for my period. Both test were postive but faint line. So I got more to take and for three days in a row I kept getting negative. I work every week all week to be able to go to the dr for a blood. And the urgent care told me that there tests were no different than I'd be able to get otc. And if there wasn't an issue otherwise that I shouldn't really have to be seen there and it can wait for a dr office. Which my work hours don't allow. But I picked up two more and their negative. But still no period. Anyone have any idea why some would be negative and some positive?