What Causes Heavy Bleeding With Abdomen Pain During The Menstruation?

hi
I have been having heavy periods for as long as i can remember.But when my periods started going over a month my GP first gave me tranexamic tablets.at first it worked but then it didn't so she put on pill [crisanta].First few days i did not have any side effects but for the past one week i have started bleeding again and i have severe stomach pain.I dont know what the problem is.I also have hypothyroidism and i am taking tablets for it.Do you think there is something seriously worng.