I have always had the same problem with my menses. Miss a month, two in one month etc. They changed pills on me all the time, it didn't work either. Just like SurgiMenopause said in her response, I had an MRI done, I have a pituitary gland tumor. They found it when I was 16, im 24 now, and said it is why my menses are all over the place and they will never be right unless they remove the tumor, even then there is no gaurantee they will be normal. The tumor is actively growing so someday I will have to have it removed but I can tell you, it has caused me to have numbness in my extremities, especially my hands because I can't even write a sentence without them going numb, along with changes in my vision and frequent headaches. I also have problems with depressive moods. A tumor on your pituitary causes all of that plus more depending the size and exact location on the pituitary it is. You should definently talk to your doctor and see about getting an MRI with contrast done of your head.
Have they done an MRI with and without contrast of your pituitary to check for a tumor? Have they checked your blood iron level, ferritin, and total iron binding capacity (TIBC) to see if you have iron deficiency from blood loss?