Boxcollider not dealing damage unless moving | Unity2D

I'm trying to set up an "attack" using boxcolliders, I've set up so that the collider attached to the player character becomes active when you press a button and is supposed to take health from a object tagged as enemy, but the enemy only takes damage when its moving into the active collider or vice versa, but not when stationary.

these are my scripts:

  public class PlayerAttack : MonoBehaviour {

     private bool attacking = false;
 
     private float attackTimer;
     private float attackCd = 0.3f;
 
     public Collider2D attackTrigger;
     
     void Start () {
         //turns off hitbox collider at start
         attackTrigger.enabled = false;
     }
     
     // Update is called once per frame
     void Update () {
         if(Input.GetKeyDown("k") && !attacking)
         {
             attacking = true;
 
             attackTimer = attackCd;
 
             //turns on hitbox collider if
             attackTrigger.enabled = true;
         }
 
         if (attacking)
         {
             if(attackTimer > 0)
             {
                 //subtracts to countdown the cooldown timer
                 attackTimer -= Time.deltaTime;
             }
             else
             {
                 //turns off hitbox collider after attack
                 attacking = false;
                 attackTrigger.enabled = false;
             }
         }
     }
 }
 

 public class AttackTrigger : MonoBehaviour {
 
     public int dmg = 20;
 
     private void OnTriggerEnter2D(Collider2D col)
     {
         if (col.isTrigger != true && col.CompareTag("Enemy"))
         {   
 
             col.SendMessageUpwards("Damage", dmg);
         }
     }
 
 
 }
 

 public class EnemyBehavior : MonoBehaviour {
 
     public float currHealth;
 
     // Update is called once per frame
     void Update () {
         if(currHealth <= 0)
         {
             Destroy(gameObject);
         }
     }
     
     public void Damage(int damage)
     {
         currHealth -= damage;
     }
 }

EDIT: Here is the movement script

 public class PlayerMovement : MonoBehaviour {
     public float movementSpeed;
     public float jump;
     public Rigidbody2D rb;
     public bool onGround = true;
     public float dblJmp = 0f;
     public float dashSpeed;
     public float dashTime;
     public float dashInc;
     public float dashMax;
     // Use this for initialization
     void Start () {
         
     }
 
     
     void Update() {
         //moves player right
         if (Input.GetKey("d") || Input.GetKey(KeyCode.RightArrow))
         {
             transform.Translate(Vector3.right * Time.deltaTime * movementSpeed);
     
             if (Input.GetKeyDown("j"))
             {
                 rb.AddForce(transform.right * dashSpeed);
                 rb.velocity = Vector3.zero;
             }
 
         }
         //moves player left
         if (Input.GetKey("a") || Input.GetKey(KeyCode.LeftArrow))
         {
             transform.Translate(Vector3.left * Time.deltaTime * movementSpeed);
     
             if (Input.GetKeyDown("j"))
             {
                 rb.AddForce((-1 * transform.right) * dashSpeed);
                 rb.velocity = Vector3.zero;
             }
         }
         //makes player jump and double jump and checks if player is on ground before allowing jump
         if ((Input.GetKeyDown("w") || Input.GetKeyDown(KeyCode.UpArrow)) && (onGround == true) /*&& (dblJmp < 2)*/)
         {
             //sets velocity of jumping player to zero before jump to make jump height consistent 
             rb.velocity = Vector3.zero;
     
                 rb.AddForce(transform.up * jump);
             dblJmp++;
         }
     
         if (dblJmp < 2)
         {
             onGround = true;
         }
         else
         {
             onGround = false;
         }
 
 
 
          }
     //checks if player is on the ground, and sets double jump counter to zero if on ground
     private void OnCollisionEnter2D(Collision2D collision)
     {
         if (collision.gameObject.CompareTag("Ground"))
         {
             dblJmp = 0f;
             onGround = true;
         }
     }
     private void OnCollisionExit2D(Collision2D collision)
     {
         if (collision.gameObject.CompareTag("Ground"))
         {
             onGround = false;
         }
     }
 }