There can be several causes of weight loss including thyroid imbalance, improper diet, lack of appetite, anemia, liver disorders etc. Since you had this problem for a long time, I would recommend that you see your doctor for some blood tests including CBC, thyroid profile, BMP, liver and kidney function tests. If a cause is found, appropriate treatment can be started. Also I would recommend daily multivitamins and iron supplements.
Regards.
Dr. G
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