These are the most common cause of bleeding in between periods. If you are on the birth control pill or a similar, hormone emitting contraceptive like the NuvaRing or Mirena coil, that is the first place you should look if you are bleeding in between menstrual "periods", which are artificial on these contraceptives. Bleeding during the middle of your cycle is not that unusual a side effect, and usually not anything to be concerned about.
Other causes of mid-cycle bleeding can include:A miscarriage, even if you were not aware you were pregnant. Miscarriages tend to start with light bleeding and cramps, and then turn into heavy bleeding and "mini labors" with rhythmical cramps. Eventually, tissue will be expelled. Ovulation bleeding, which lasts for a short time and is very light. Implantation bleeding, if you conceived that month. This normally happens a week to 12 days following ovulation. A sexually transmitted disease, like chlamydia. If you have any reason to suspect that you could have an STD, do get tested, as treatment is easiest in the early stages. Cervical or uterine cancer, though the latter is very unusual in women who are still menstruating. An ectopic pregnancy can cause vaginal bleeding. If you have any reason to think you may have an ectopic pregnancy on your hands, please contact a doctor immediately. Rough sex can cause bleeding sometimes, but there should not be a lot of blood. Starting the menopause. Suffering from Polycystic Ovary Syndrome.