Why is my period 11 days late and I normally get them on a regular basis and have never missed one

Sometimes changes in your diet and even in your lifestyle can cause irregularity in your period. If it ends up being too long, check with your doctor.

Women at time just get off one month, late, or even miss one. Many things can cause it.

Of course you placed it under pregnancy, so if you are having sex, you could also be pregnant. SO- have you taken a pregnancy test if you are sexually active?