According to the symptoms you reported, there are several possible explanations for the bleeding after sexual intercourse. If the bleeding was immediately after the sexual intercourse, then it might have been caused by insufficient lubrication that caused too much friction and lesions in the vaginal walls. If the bleeding occurred few days after the intercourse it might be due to bacterial infection. The itching might be related to the infection, too. Vaginal smear might be able to detect the bacteria and adequate antibiotic might be recommended by your gynecologist.
The bleeding is less likely to have been implantation bleeding because it would have been expected to end within several days. However, pregnancy can not be ruled out without examination by gynecologist.