could I be pregnant

Okay so I'm 7 days late for my period and I have taken 5 test each has been nagative. But my mom didn't find out she was pregnant with me till 15 days after her period was late. Is it possible that I am? Is there anything other then pregnancy and stress that can cause my period to be this late. I can't have a baby yet I'm 19 but just not ready and neither is my BF.