My body has been bruising for no reason at all they just appear everywhere this has been happening for the last four weeks why?

Low platelets? You should see your doctor for some screening blood tests. Based on your age, one of the most common reasons for your symptoms is low platelets caused by auto-antibodies. Sometimes this goes away on its own, other times it needs treatment. There are other causes of low platelets, and there are other causes of bruising not associated with platelets. See your doctor.