Abnormal bleeding may stem from multiple causes that aren’t serious, among them, perimenopause or uterine fibroids or polyps. Thyroid problems can affect the menstrual cycle, too, Puritz says. In nursing mothers and postmenopausal women, vaginal dryness, combined with friction, can cause spotting after intercourse.But if you bleed every time after sex, “that’s a worrisome sign that the cervix is being easily irritated and usually, it often does that if there’s some infection of the cervix, Puritz says.bnormal bleeding may stem from multiple causes that aren’t serious, among them, perimenopause or uterine fibroids or polyps. Thyroid problems can affect the menstrual cycle, too, Puritz says. In nursing mothers and postmenopausal women, vaginal dryness, combined with friction, can cause spotting after intercourse.