2D player damage on trigger collider - unity3d

Question

So I'm making a little top down space shooter and everything works great so far. My issue is that when I change weapons I would like the secondary to do more damage than the primary (changeable with the number keys). It's been a real head scratcher and any help would be greatly appreciated. this is what I tried;
adding the weapons to individual layers. in the OnTriggerEnter2D function I make an if statement stating if the gameObject (bullet) is firing from layer 13, take away x amount of HP. Doesn't do anything though. below is my current code for the enemy.
using UnityEngine;
using System.Collections;
public class enemyDamage : MonoBehaviour {
public int health = 2;
void OnTriggerEnter2D(){
health--;
}
void Start () {
}
void Update () {
if (health <= 0){
Die();
}
}
void Die(){
Destroy (gameObject);
}
}

Answer 1

You can change your OnTriggerEnter2D function by adding Collider2D parameter to it. That way you can get access to the gameObject that triggered the function.
You didn't post the code that is instantiating the bullet. But if you set bullets name to different values you can decrease the health based on that.
void OnTriggerEnter2D(Collider2D other) {
if(other.gameObject.name == "missile"){
health -= 10;
}else if(other.gameObject.name == "bullet"){
health -= 1;
}
}
Or even better idea might be adding a script to the bullet, which knows the amount of damage the bullet is going to make.
void OnTriggerEnter2D(Collider2D other) {
health -= other.gameObject.GetComponent<BulletScript>().damage;
}