I'm underweight however having belly. what is the reason and how to overcome ?

Underweight: I understand your concern for the belly. Underweight can be due to lack of Balanced Diet or Medical Condition or stress. Belly could be due to lack of exercise and lack of toning of muscles. See your Physician for diagnosis and treatment along with a Nutritionist to guide you for Healthy Diet. See a Therapist to understand stressors in your life, its effect on your body and mind and how to cope.