you had your period which lasted foe 3 to 4 days (instead of usual 7 days) a week ago.
You had coitus 4 days after your period, because of which you had bleeding also.
So far every thing is fine. You have bleeding once again 7 days later to the previous period.
Usually at this age bleeding in between the menstrual cycle is called Dis functional Uterine Bleeding
(DUB).Abdominal scan, relevant blood investigation.a smear or Biopsy
as per Gynecologist opinion is advised