Player sometimes doesnt jump Instantly when clicked

I made a platformer game, where the player has to reach the end to pass the level. The player is a SPHERE BALL. My problem is when the ball roles it sometimes does not jump when the screen is clicked. I tried putting the player movement into void FixedUpdate(), instead of void Update(). The player still doesnt jump instantly, i checked all my ground colliders and there isnt any problems. Im not sure what the problem is. Any ideas? Many thanks

using UnityEngine; using System.Collections; using UnityEngine.SceneManagement;

 public class PlayerControl : MonoBehaviour
 {
     //COMPONENTS
     private Rigidbody2D myRigidbody;
     private CircleCollider2D myCollider;
 
     //SPEED/JUMP
     public float moveSpeed;
     private float moveSpeedStore;
     public float jumpForce;
 
     public float jumpTime;
     private float jumpTimeCounter;
 
     private bool stoppedJumping;
     private bool canDoubleJump;
 
     //GROUNDED
     public bool grounded;
     public LayerMask whatIsGround;
 
 
     // Use this for initialization
     void Start()
     {
         myRigidbody = GetComponent<Rigidbody2D>();
         myCollider = GetComponent<CircleCollider2D>();
 
         speedMilestoneCount = speedIncreaseMilestone;
 
         moveSpeedStore = moveSpeed;
         speedMilestoneCountStore = speedMilestoneCount;
         speedIncreaseMilestoneStore = speedIncreaseMilestone;
 
         jumpTimeCounter = jumpTime;
 
         stoppedJumping = true;
     }
 
     void FixedUpdate()
     {
         grounded = Physics2D.IsTouchingLayers(myCollider, whatIsGround);
         /*grounded = Physics2D.OverlapCircle(groundCheck.position, groundCheckRadius, whatIsGround);*/
 
         myRigidbody.velocity = new Vector2(moveSpeed, myRigidbody.velocity.y);
 
         if (Input.GetMouseButtonDown(0))
         {
             if (grounded)
             {
                 myRigidbody.velocity = new Vector2(myRigidbody.velocity.x, jumpForce);
                 stoppedJumping = false;
             }
             if (!grounded && canDoubleJump)
             {
                 myRigidbody.velocity = new Vector2(myRigidbody.velocity.x, jumpForce);
                 jumpTimeCounter = jumpTime;
                 stoppedJumping = false;
                 canDoubleJump = false;
             }
         }
         if ((Input.GetMouseButton(0)) && !stoppedJumping)
         {
             if (jumpTimeCounter > 0)
             {
                 myRigidbody.velocity = new Vector2(myRigidbody.velocity.x, jumpForce);
                 jumpTimeCounter -= Time.deltaTime;
             }
         }
         if (Input.GetMouseButtonUp(0))
         {
             jumpTimeCounter = 0;
             stoppedJumping = true;
         }
         if (grounded)
         {
             jumpTimeCounter = jumpTime;
             canDoubleJump = true;
         }
     }
 
     // Update is called once per frame
     void Update()
     {
         //SPEED MULTIPLIER CODE HERE
     }