you didn't mention on exactly which day of cycle your menstruation
in case of regular cycles the period between 8th to 20th day of cycle will be taken as fertile period.
so if the days you had intercourse comes into that period there are chances of pregnancy
the other causes could be,
-small post coital tear, which might have led to little spotting and pain,
-premenstrual syndrome- where breast tenderness and fullness, abdominal pain
etc features can be seen.
you wait till your period date and take pregnancy test to rule out the cause.