Hi,
Welcome to the ehealthforum and I am glad to help you out. Bleeding after unprotected intercourse two days after your periods is due to old menstrual blood coming out. If the repeat episodes happen then intermenstrual spotting and intermenstrual bleeding have to be ruled out.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For an exact diagnosis, you are advised to consult your doctor. I sincerely hope that helps. Take care.