Unity5 rigidbody2d not working properly... :(

I have a playercontroller script that handles the gravity and jumping of the player.. but what happens is the player is bearly jumping and falling. But my script is fine with unity4, after i upgrade my game on unity5 the problem occurs... please help.. There is a function applygravity there and jump function you can ctrl+f to search, sorry for the mess :)

note: no other script is handling my physics for the player except this playercontroller script

by the way my game is like flappy bird style...

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 /// <summary>
 /// the logic of the gameloop of this class
 /// </summary>
 /// <returns></returns>
 IEnumerator OnUpdate()
 {
     //start catching  if the user taps the screen
     StartCoroutine("CheckTap");

     //do this only if the player is not dead
     while (true)
     {
         switch (playerState)
         {
             case PlayerState.Idle:
                 break;
             case PlayerState.Flying:
                 //when the player is not on the ground
                 if (!groundCheck.IsGrounded || GameController.Instance.debugMode)
                 {
                     //do the calcualtions on the air
                     DoAirLogic();

                     //dont let the player go up offscreen 
                     RestrictVerticalPosition();
                 }
                 break;
             case PlayerState.Dead:
                 //stop checking if the player is dead
                 StopCoroutine("CheckTap");
                 playerAnimator.PauseAnimation();
                 DidTap = false;
             if (groundCheck.IsGrounded && !isDead && rigid2D.velocity == Vector2.zero)
                 {
                     isDead = true;
                     //playerState = PlayerState.Idle;
                     StartCoroutine("DeathState");
                 }

                 break;
             default:
                 break;
         }
  
         //apply gravity
         ApplyGravity();
         //wait for the fixed update
         yield return new WaitForFixedUpdate();
     }
 }

   

 #region player air and ground logic calculation
 /// <summary>
 /// this is where the calulations or logics when the player is not on the ground
 /// </summary>
 void DoAirLogic()
 {

     //when the user taps the screen
     if (DidTap)
     {
         DidTap = false;
         //cast a ray from the touch points on the screen to test if we tap on a powerups
         RaycastHit2D touchHit = Physics2D.Raycast(Camera.main.ScreenToWorldPoint(Input.mousePosition), Vector2.zero);

         //if the user tap on a powerup
         if (touchHit.collider != null)
         {
             if (touchHit.collider.gameObject.tag == "powerup")
             {
                 //get the powerups from the container and use it
                 PowerUpContainer pu = touchHit.collider.gameObject.GetComponent<PowerUpContainer>();
                 pu.ApplyMyPower();
             }
         }

         //makes the player jump
         Jump();
     }

     //rotate the player  up wars if the player is going up or downwards if the player is giong down but only if he is grounded
     //if (!groundCheck.IsGrounded)
       //  DoRotation();
 }

 /// <summary>
 /// Apply the gravity only if it is enabled
 /// </summary>
 void ApplyGravity()
 {
     //if we can use gravity
     if (EnableGravity)
     {
         //apply gravity only when we are not on the ground
         rigid2D.AddForce(new Vector2(0.0f, -gravity));
     }
 }

 /// <summary>
 /// This makes player jump
 /// </summary>
 void Jump()
 {
     //play the jump sound
     GetComponent<JumpSound>().PlayOnce();

     //make a jumpfore vector based on the jumprate set on the inspector
     Vector2 jumpFoce = new Vector2(rigid2D.velocity.x, jumpRate);

     //reset the current velocity of the player
     //we do not want to add up this jumpforce velocity to the current velocity of the player
     rigid2D.velocity = Vector2.zero;

     //apply the velocity to our rigidbody
     //this makes the player to jump
     rigid2D.AddForce(jumpFoce,ForceMode2D.Force);
 }
 #endregion