no period

so the predictor told me my period should b here yesterday and it never came.. last month my period came on the 3rd and the 27th bt the 27th didnt seem normal to me so i took a test it said pos, bt then i took more an they came out neg. so today since im a day late i took a test an it showed pos, bt would if its wrong again.. n i took a dollar tree test an those are pretty accurate before when i took them they only showed neg so today was my first pos from this tese