The bleeding after sex can be due to various causes like :
1) an infection such as pelvic inflammatory disease
(PID) or a sexually transmitted infection (STI) such as chlamydia.
2)vaginal dryness (atrophic vaginitis
) 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.
3) cervical or endometrial polyps (benign or non-cancerous growths in the womb or the lining of the cervix)
4) cervical erosion, where there is an inflamed area on the surface of the cervix (neck of the womb)
You should have the vaginal smaer examination done to rule out any genital infection
as it may commonly cause such bleeding after sex associated with irregular periods
.The other causes should also be ruled out.
The treatment is according to the underlying cause.The oral antibiotics
may be required to control the infectious cause.