Welcome to HCM,
After going through your history, I can not understand what made you think regarding pregnancy
because if your period is there and did not had unprotected sex.
If you do not remember your date and if you think date is already passed and had protected sex there could be rare possibility hence kindly do a Urine pregnancy test and if negative then wait for week and repeat the test.
You should know irregular period can be due to stress,severe anemia
, may be the cause once pregnancy is ruled out.
Regarding symptoms of tiredness
can be due to various disease like anaemia
so please visit your Physician to examine and find out if there is any thing which requires to be taken care off.
If you are not sexually not active then just take care of your health and do not worry.
Please take care