Implantation Cycle Case Study

I understand your concern
If you did sex during fertile phase of period then you should think about implantation bleeding.
Following are features of implantation bleeding:
Occur around at the time of period date
Very mild just like spotting
Just for 1-2 days
Associated with mild abdominal cramp for 1-2 days. pink to brownish colour

Menstrual bleeding is more , red in colour
If abdominal cramp will increase continuously then it is menstrual bleeding

I would suggest to go for urine PREGNANCY test or blood HCG test to confirm PREGNANCY once period will be delayed by more than seven days from normal expected period date.
Avoid stress, take healthy diet, drink plenty of water and do regular exercise
Hope this may help