Having problems when using triggers

Hello all, am having a problem when I want use the OnTriggerEnter method. So basically I have a list of information(questions) and I want to get a random question every time when the player enters the trigger, but I get spammed all the questions really fast instead. I didn't manage to solve this problem so here is my code. I will be really thankful if somebody helps me.

 public int width = 800;
         public int height= 300;
         public bool showWindow = false;
         public bool gameOver = false;
         public System.Collections.Generic.List <question> questions;
         [Space(10)]
         private playerController pc;
         //private string countryName;
 
         //private int score = 0;
         private int randomNumber;
 
         void Start () {
             pc = GetComponent<playerController> ();
         }
 
         void OnGUI () {
             /*if (Input.GetAxis ("Q") > 0) {
                 randomNumber = Random.Range (0, questions.Count);
                 showWindow = true;
             }*/
             if (showWindow) {
                 randomNumber = Random.Range (0, questions.Count);
             GUI.Window (0, new Rect (Screen.width / 2 - width/2, Screen.height / 2 - height/2, width, height), WindowFunction, questions [randomNumber].questionName);
                 Screen.lockCursor = false;
                 pc.lockScreen = true;
             }
         }
 
         private void OnTriggerEnter (Collider collider) {
             //this.countryName = collider.gameObject.name;
             if (collider.gameObject.name == "Trigger") {
                 showWindow = true;
             }
         }
 
         private void OnTriggerExit (Collider collider) {
             if (collider.gameObject.name == "Trigger") {
                 showWindow = false;
                 pc.lockScreen = false;
                 Screen.lockCursor = true;
             }
         }
 
         private void rightAnswer () {
             int rnd = Random.Range (1, 50);
             int a = 0;
 
             switch (questions[randomNumber].difficulty) {
                 case 1: a += 100 + rnd;
                         break;
                 case 2: a += 300 + rnd;
                         break;
                 case 3: a += 700 + rnd;
                         break;
                 }
 
             pc.score += a;
             showWindow = false;
             pc.lockScreen = false;
             Screen.lockCursor = true;
         
         }
 
         private void wrongAnswer () {
             if (pc.lives > 0) { 
                 pc.lives -= 1;
                 showWindow = false;
                 pc.lockScreen = false;
                 Screen.lockCursor = true;
             }
 
             if (pc.lives <= 0) {
                     Application.LoadLevel ("Game over");
                     gameOver = true;
             }
         }
 
         private void WindowFunction (int windowID) {
             if (GUI.Button (new Rect (50, 20, 600, 30), "A) " + questions [randomNumber].answerA)) {
                     if (questions [randomNumber].answerRight == 1) {
                             rightAnswer ();
                     } else {
                             wrongAnswer ();
                     }
                 
             }
             
                 if (GUI.Button (new Rect (50, 55, 600, 30), "B) " + questions [randomNumber].answerB)) {
                     if (questions [randomNumber].answerRight == 2) {
                             rightAnswer ();
                     } else {
                             wrongAnswer ();
                     }
                 }
             
                 if (GUI.Button (new Rect (50, 90, 600, 30), "C) " + questions [randomNumber].answerC)) {
                     if (questions [randomNumber].answerRight == 3) {
                             rightAnswer ();
                     } else {
                             wrongAnswer ();
                     }
                 }
             
                 if (GUI.Button (new Rect (50, 260, 600, 30), "Exit)) {
                     showWindow = false;
                     pc.lockScreen = false;
                     Screen.lockCursor = true;
 
                 }
 
         }