Thanks for the query.
Menstrual cycle can get altered by many things.
Some of them are poly cystic ovary disease, recent illness, weight changes, thyroid
If you had unprotected intercourse
during the time of ovulation, then go for blood test
once. That will rule out the possibility of pregnancy.
Then you consult gynecologist once and get examined to find out the possible cause for your problem and take treatment accordingly.