Vaginal bleeding after intercourse during 4 months of breastfeeding may be related to menstruation, vaginitis, cervical lesions, etc., and you should consult a doctor in time to find out the cause. 1. Menstruation: Many women will have their menstruation around 3-6 months after giving birth, and when they have intercourse, they just bump into their menstruation and experience vaginal bleeding. 2. Vaginitis: due to vaginal inflammation, the brittleness of vaginal tissues increases, and at the same time, inflammation will lead to inflammation of the vagina, dysfunction of the normal flora of the vagina, edema of the vaginal walls, easy to rupture and bleeding and accompanied by vaginal pain. 3. Cervical lesions: cervical lesions, there will be vaginal bleeding after intercourse, it is recommended to do cervical TCT and HPV examination, according to the results of the appropriate treatment. There may be other reasons for vaginal bleeding after intercourse during 4 months of breastfeeding, so it is recommended to consult a doctor in time to get a clear diagnosis and treatment as soon as possible.