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Considering your age and nature of symptoms, I would consider possibility of anxiety disorder first in your case.
Common symptoms of anxiety which may or may not be present in your case: nervousness
, mild irritability, excessive worry regarding own health, tremor, muscle spasm, heaviness in body, easy fatigability, headache, sleep disturbance, palpitation
and dry mouth.
Out of them you mentioned restlessness, tremors and poor concentration. These symptoms increases during stress. As you have symptoms for years then possibility of ADHD need to be ruled out too by examination by psychiatrist
Till you meet psychiatrist, following simple measures will help you:
-Healthy diet: Milk and fruits in diet.
-Daily morning walk
, yoga and meditation (which you can learn from some expert in person)
Wish you Good Health and all the best.