What i can do when i am nervous ?

Exam and consult: see your physician and get examined. There are multiple causes of anxiety.

Well...: You should learn relaxation techniques. Find the triggers and if possible avoid them

Relax.: But that is easier said than done. Practice deep breathing exercises and learn to calm yourself. Try and avoid stressful situations that have caused symptoms before. Talk to a doctor and/or counselor either professionally or church/synagogue if religious. Jumping to medication as a first choice is usually not the best first option. A good doctor/counselor/friend will help you through this.

To address stress:: If you can find a quiet place - do so. Breath in slowly & deeply through your nostrils. Fill your lungs with air (but not to the point of discomfort). Hold for a count of five then slowly begin to exhale through an open mouth. Repeat at least 12 times, longer if you need to.