Hi thanks for your question.
How sex is possible with 4 years old boy friend? Probably a typing mistake. No this cannot be Implantation
bleeding, implantation bleeding occurs approximately one week after fertilization and remains for 1 to 2 days and not for 12 days. Most probably you have developed infection from your boy friend may be a sexually transmitted disease
. Consult a gynecologist who may examine you to determine the type of infection you have developed. She/he may take swab from your vagina for culture and may prescribe you appropriate treatment.
Hope this answers your question.