Thanks for your question on Healthcare Magic.
I can understand your concern.
Decreased appetite in young patients is mostly due to
tuberculosis, anemia, thyroid diseases etc.
So better to
consult doctor and get done clinical examination, chest x ray, hemoglobin estimation and thyroid function test.
If any of the above mentioned report is abnormal then you have to start treatment accordingly.
If all reports are normal then
consult psychiatrist to rule out depression as undiagnosed depression can also cause similar symptoms.
So consult psychiatrist and get done
counselling sessions. Try to identify stressor in your life and start working on its solution.
You may need
anti depressant drugs too.
Don't worry, you will be alright.
Hope I have solved your query. I will be happy to help you further. Wish you good health. Thanks.