What Causes A Delayed Menstrual Period With Negative HPTs?

Hi 22 jul was my last peroids day and now its 23 august n im having pain in utreus for the last 12 days feeling nasuea and brests are tenders and tried three urine test with strips at home and they all were negative . Now i want to know that why my cycle is delayed coz it never happened before. So plz help me to tell me am i pregnanet or not. Feeling anxiety about it.