Having an issue with using an Enum and using a string variable

Hello all, I'm trying to use a switch statement with an enum. what I using it for is i have a gameObject itemPickUp and in the script i have:

 public string itemType;                // string to store the item name.
 public int inventoryAmountToAdd;       // an int to store the amount to add to the inventory.

 void Start () {
     playerScript =  GameObject.FindGameObjectWithTag("Player");        // Finds the target by the tag assigned to the game object.
 }

 void OnTriggerEnter(){
     playerScript.GetComponent<Player>().PickUp(itemType, inventoryAmountToAdd);
     Destroy(gameObject);
 }

That part works, but in the Player.cs script in the PickUp() function:

 public void PickUp(string item, int amount){
     switch(item){
     case itemPickUps.SMALLHEALTH:
             break;
     case itemPickUps.MEDIUMHEALTH:
             break;
     case itemPickUps.LARGEHEALTH.ToString():
             break;
     case itemPickUps.SMALLSTAMINA.ToString():
             break;
     case itemPickUps.MEDIUMSTAMINA.ToString():
             break;
     case itemPickUps.LARGESTAMINA.ToString():
             break;
     case itemPickUps.PISTOLAMMO.ToString():
             break;
     case itemPickUps.RIFLEAMMO.ToString():
             break;
     case itemPickUps.PISTOL.ToString():
             break;
     case itemPickUps.RIFLE.ToString():
             break;
     case itemPickUps.PLASMASWORD.ToString():
             break;
         default:
             break;
     }// end of switch(itemPickUps)
 }

as you see in the first two cases I've tried just using the enum and then the name but it gives the error Cannot implicity convert type 'Player.itemPickUps' to string, so I've tried using the .ToString() method and get the following error A constant value us expected.

If anyone could help me with this it would be greatly appreciated.