Could i be pregnant?? Help

Shannie
My period was pose to be due the 24th!!Then it said the 26th nothing yet then it said it'll be coming today the 28th nothing still!!I had a positive ovulation test on March the 9th but I had positive ovulation tests for almost two weeks but everytime I take a test its negative and the month is almost over and I don't know what to do I'm having such bad back pain anyone know any suggestions please let me know