Polygon Collider 2D Problem.

Okay so basically my main character uses a sword to attack and I have made a polygon collider around it to use for collisions against enemies. Everything is set up, but when I attack, multiple enemies take damage at the same time instead of just one. It's very confusing and I haven't been able to solve this problem. Here is the polygon collider script

 using UnityEngine;
 using System.Collections;
 
     public class HeroHitBoxManager : MonoBehaviour {
     
         // Set these in the editor
         public PolygonCollider2D frame2;
         public PolygonCollider2D frame3;
         public PolygonCollider2D frame4;
     
         // Used for organization
         private PolygonCollider2D[] colliders;
     
         // Collider on this game object
         private PolygonCollider2D localCollider;
     
         // We say box, but we're still using polygons.
         public enum hitBoxes
         {
             frame2Box,
             clear // special case to remove all boxes
         }
     
         void Start()
         {
             // Set up an array so our script can more easily set up the hit boxes
             colliders = new PolygonCollider2D[]{frame2};
     
             // Create a polygon collider
             localCollider = gameObject.AddComponent<PolygonCollider2D>();
             localCollider.isTrigger = true; // Set as a trigger so it doesn't collide with our environment
             localCollider.pathCount = 0; // Clear auto-generated polygons
         }
     
         void OnTriggerEnter2D(Collider2D col)
         {
             Debug.Log("Collider hit something!");
         }
     
         public void setHitBox(hitBoxes val)
         {
             if(val != hitBoxes.clear)
             {
                 localCollider.SetPath(0, colliders[(int)val].GetPath(0));
                 return;
             }
             localCollider.pathCount = 0;
         }
     }

And here is the health script.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.SceneManagement;
 
 public class HealthScript : MonoBehaviour {
 
 
 
     private GameMaster gm; 
 
     public bool isEnemy = true;
     public float max_Health = 100f; 
     public float cur_Health = 0f; 
     public GameObject healthBar; 
 
     void Start()
     {
         gm = GameObject.FindGameObjectWithTag ("GameMaster").GetComponent<GameMaster> (); 
         cur_Health = max_Health;
         InvokeRepeating ("decreaseHealth", 1f, 1f);
     }
 
     void Update()
     {
         
     }
 
     void decreaseHealth()
     {
         
         //uncomment if you want to test health bar. 
 
         
         float calc_Health = cur_Health / max_Health;
         SetHealthBar (calc_Health);
      
     }
 
     public void SetHealthBar(float myHealth)
     {
         healthBar.transform.localScale = new Vector3 (myHealth, healthBar.transform.localScale.y, healthBar.transform.localScale.z);
     }
 
     // Update is called once per frame
     void OnTriggerEnter2D (Collider2D collider) 
     {
 
         HeroHitBoxManager hit = collider.gameObject.GetComponent<HeroHitBoxManager> ();
         hit = null; 
         if (hit != null && gameObject.tag == "Enemy") 
         {
             cur_Health = cur_Health - 5; 
         }
             if (cur_Health <= 0 && gameObject.tag == "Enemy") {
                 Destroy (gameObject);
                 gm.points -= 1;
                 
                 if (gm.points == 0){
                     SceneManager.LoadScene("WinScreen");
                 }
                     
             }
             if(cur_Health <= 0 && gameObject.tag == "Player"){
             Application.LoadLevel("YouLose"); 
             }
     }
 
 void OnCollisionEnter2D (Collision2D col)
 {
     //Check collision name
     Debug.Log("collision name = " + GetComponent<Collider2D>().gameObject.name);
         if(col.gameObject.tag == "Enemy")
     {        
             cur_Health = cur_Health - 5;     
     }
 
     }
 }