What Is The Reason Behind Abnormal Vaginal Bleeding?

Hi,i am 22 yrs old girl,i am having menstrual bleeding since 25days and my weight is 70kgs.I am suffering from thyroid and under medication.My cycles are always irregular..doctors have prescribed me to lose weight.I am also taking progesterone tablets for 14days which doctor gave me in order to make it regular.she also prescribed me to have tranostat after knowing about my irregular lasting of menstrual cycle but it didn't worked at all.gradually the flow increased and now it's 25thday,should i continue with those progesterone tablet(3 left)???what is the reason behind this abnormal bleeding?please help!!!