Hi I Have Problem My Last Menstrution Is March 15

Hi i have problem my last menstrution is march 15 2016 im expecting april 15 2016 but now may 2 ready still not yet come i test pregnancy test 6x ready result is negative the 2 same brand of pregnancy test show have 1 very red line at C and have not so red line T and the 4 same brand pregnancy test is only 1 very redline C i want to ask how is that im pregnant or negative ?thank u