Thanks for the query.
The possible causes for your scanty flow are:
Hypomenorrhea: scanty menstrual flow. Can be seen in conditions like anemia, poly cystic ovary disease, thyroid disorders, weight changes etc.
also spotting can be seen on expected period dates as the gestational sac
will not completely obliterate the uterine cavity
in early pregnancy.
So if there is possibility of pregnancy means you had unprotected intercourse
around the time of ovulation, better to get examined once to rule out the pregnancy.