What Causes Prolonged Menstrual Bleeding?

Hi i usually have a clockwork and normal period, but this time my period came on time but is still happening even now making this the 13th day, also like the 3rd day of the period i started going to the bathroom uncontrollably every 2 1/2 hrs tho that has reduced now and usually felt uncomfortable after it as tho i wanted to go to the bathroom right away afterwards...i went to a doc who told me her hands are tied basically that to drink more diluted cranberry juice, poked my stomach and then said since she cant test my urine she believes it might be a cysts..i need to know if this is a possibility and what are the other possible things it could be cause right now im freaked