Question About Chronic Anaemia.?

Does anyone have any ideas of what might cause chronic anemia? I have hypothyroidism and am on hormone replacement therapy. I have been under treatment sporadically for anemia since I was about 7, and I'm 35 now. It seems like I become anemic every time I stop taking iron supplements. It's as if my body lacks the ability to store iron. Could my history of anemia be related to my current situation? My doctor is sending me for an ultra sound to see if the cause could be fibroids, but I'm doubtful because I've had this since before I began menstruating. I also doubt it is dietary, because I eat red meat 7 days a week. I've been tested for just about everything from lupus to pernicious anemia, and nothing has turned up. I've tried researching articles, but there isn't anything on childhood anemia that doesn't eventually clear up. The only time I'm not anemic is when I've taken high doses of iron supplements, but this only helps for a month or two, then I'm anemic again.