Thanks for your question.
If your previous cycles were all regular then first possibility is an early pregnancy
. You should certainly do a pregnancy test if you are late for your periods for more than 7 days to avoid false negative results. Signs of early pregnancy are not necessary for a women to be declared pregnant.
If you are not ready for a pregnancy you may discuss the option of medical abortion
with your doctor if this is legal in your country.
Try to use a reliable birth control in future if you are not ready for a pregnancy.