There are many reasons why a woman may bleed after sex. The medical name for this is "postcoital bleeding".
Most common is an infection, such as pelvic inflammatory disease
(PID), or a sexually transmitted infection (STI), such as chlamydia then vaginal dryness
) caused by reduced vaginal secretions after the menopause
, damage to the vagina, such as tears caused by childbirth, or by dryness or friction during sex or cervical or endometrial polyps (benign or non-cancerous growths in the womb or the lining of the cervix
If the problem is caused by vaginal dryness, they may recommend that you try using lubricating gels. For other treatments, it would be necessary to see a gynecologist and establish the right cause first.
Hope I have answered your query. Let me know if I can assist you further.
Dr Ivan R. Rommstein, General Surgeon