Bruising is caused from broken blood vessels, which occurs from some instance of trauma. You probably bruise very easily and just do not realize when the trauma occurs, which is common for people in your position. People who bruise easily have blood coagulation problems. Blood clotting is an extremely complex mechanism that involves a number of chemical reactions involving the blood platlets. A number of these chemicals are produced in the liver. People with liver disease are known to bruise easily. So, your problem could be as simple as having a vitamin deficiency or as severe as having a genetic, liver or auto-immune disease. I would advise that you see your physician as soon as you can to get a full blood workup.