Welcome to HCM,
You are definitely underweight
and one of the possible cause for loosing weight in spite of good diet and appetite is hyperthyroid state,Diabetes
is another such condition.
You have sleeplessness
and signs of increased metabolic rate hence you should see a good Physician/Endocrinologist
to find out the cause and take treatment.
In Thyroid function please get your Free T3, Free T4 and TSH which should point to the diagnosis if they come other causes should be explored,
In which biochemistry including blood glucose and possible hidden infection like TB,even hidden malignancy should be considered.