<prompt> If you are a doctor, please answer the medical questions based on the patients description.my first day of my last cycle was January 7,2014 it only lasted for at least 3-4 days then I was in a car accident on January 17, 2014 rear end from behind I have not had my period or at least what I think until February 28, 2014 and when I first notice it was brownish red on march 1,2014 started off the same way and then turn light red on march 2,2014 I wore a tampon and when I went to change it a long darkish dry rubber string of what to appear to be blood was on the tampon but barely no blood on tampon  <response>: Hi, thanks for using Chat Doctor There are different possible causes for delayed or irregular periods. If you are sexually active, you need to rule out pregnancy as a cause. The other causes are: 1 emotional or physical stress or illness2inadequate diet3abnormal level of thyroid hormone4high levels of prolactin hormone which is released in the brain5polycystic ovarian syn Chat Doctor. I hope this helps 