Hello, Bruises in the thigh are commonly due to thin skin, lack of muscle and fat to cushion the blood vessels may cause easy bruising. Take balanced diet and gain weight. Do regular exercises. However, bruising may be a sign of Leukemia. Since you feel fatigued, have headaches and a loss of appetite, you are suggested to get clinically examined by a GP. The treating GP will tell you to get blood test and bone marrow test to detect leukemia. Vitamin C or K deficiency and bleeding disorders may also cause bruises. Your treatment will depend on your symptoms and pathology detected. In the meantime, frequently use ice over the bruise for relief. You can apply calamine lotion or Soframycin cream for relieve. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician