I have red blood with clots 3 days before period due, i had sex around a week after ovulation, the blood isn't too heavy, is it just my period?

More than likely: It is very likely that bleeding you are having is your period. Both the length of the a woman's menstrual cycle and the character and amount of bleeding during menses vary now and then in most women, for a variety of reasons or for no apparent reason. If you are concerned about the possibility of pregnancy you should do a pregnancy test, and should use reliable birth control.