There is always a phase of hair falling, in which one faces the problem; so at your age don't worry this phase will go.
Have you suffered any illness recently?that can be the reason for hair falling and it will stop once you recover completely from the illness.
Next Steps
Massage your scalp with oil regularly. Check whether your shampoo or conditioner is causing hair fall.
Health Tips
Have balanced diet, proper sleep.
Your problem will be solved. You are at such a young age, I don't think you will need any medicine.