After an orgasm, it is possible to have bleeding from the vaginal cavity. Aggressive sexual intercourse or being on a menstrual cycle are both likely reasons if a penis or sex object was able to pass into the vaginal cavity but when only the clitoris is stimulated during an orgasm, blood can also flow.
In order to understand the physiological reason for this, understanding the anatomy of the vaginal and secondary organs is useful. The clitoris represents one of the most sensitive organs in the female reproductive tract and is highly innervated by the vagus nerve. When the clitoris is first stimulated, the vagus nerve is activated and redirects blood to the clitoris and vaginal cavity. The vagina becomes engorged with blood and women in essences, have an "erection" similar to what happens with the penis of a male.
Bleeding can occur afterwards regardless of whether there is any penetration into the vaginal cavity depending on the integrity of the uterine wall. This is termed postcoital bleeding and is seen in almost 10 percent of women after orgasm. During a woman's reproductive years, this is generally a common and benign condition but once a woman reaches menopause, could represent something more sinister.
During a woman's period, the tissue sloughs off the wall and bleeding occurs because these small capillaries (blood vessels) are more exposed than during the rest of the cycle. Due to clitoral stimulation, prostaglandins are released into the tissue to help the vagina prepare for sexual intercourse and may naturally lead to blood slipping into the vaginal cavity.
You do not have to be on your period in order for this process to happen. It is very common for women to also experience spotting, a normally physiological process that occurs half way through a normal menstrual cycle. This can be due to a number of innocent causes such as changing the dose of OCP that you may be taking, a new diet, stresses at work or even changes in a sleep cycle. This problem normally self-corrects but it is wise to consult with your gynecologist to determine if the dose of your oral contraceptive is too high. A speculum examination will also be preformed to make sure there are no masses within the vaginal canal that could be causing these symptoms.
When you have reached menopause, bleeding during a clitoral orgasm is something that also most likely is benign in nature, but in up to 20 percent of women, there could be malignant changes to the cervix that must be investigated. It is imperative that you consult with your gynecologist immediately because cervical cancer is the biggest worry in this case. You will need to undergo a speculum examination and most likely have a biopsy of your cervix to ensure that there is no malignant changes to the tissue. 
An unfortunate fact that I have seen myself in the gynecology wards is women forget to get their Pap smears for a prolonged period of time. Even after menopause, women are still at risk for cervical changes and sexual activity is not needed to have these irregular changes. It is recommended that women between the ages of 21 to 65 get a Pap smear done every 3 years. If irregular cells are found, it is recommended that you follow-up with another Pap smear within 1 year. This is referred to as CIN types 1, 2 and 3. Make sure you know the state of your cervix and meet with a gynecologist regularly. 
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