GetMouseButtonDown(0) is laggy

When i start a game and click more times (GetMouseButtonDown(0)) some of the clicks don’t work… i really dont know why? Is it just a lag on my PC or in unity… or it’s something with the script

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerScript : MonoBehaviour
{
private bool isInGame = false;

private bool isGameOver = false;

private Rigidbody2D myRB;
Vector2 tempPos;
private bool isRight = false;
private void Start()
{
    myRB = GetComponent<Rigidbody2D>();
}
private void FixedUpdate()
{

    if (Input.GetMouseButtonDown(0)&& isRight && !isGameOver)
        {
            tempPos = transform.position;
            tempPos.x += 2.0f;
            transform.position = tempPos;
            print("isRight");
            isRight = false;
        }



    else if (Input.GetMouseButtonDown(0)&& !isRight && !isGameOver)
        {
            tempPos = transform.position;
            tempPos.x += -2.0f;
            transform.position = tempPos;
            print("!isRight");
            isRight = true;
        }

    if (!isInGame)
        return;
}
 
public void InitGame()
{
    isInGame = true;
}
 
void OnCollisionEnter2D (Collision2D other) 
{
	if (other.collider.tag == "Enemy") 
	{
		FindObjectOfType<GameScene>().GameOver();
		FindObjectOfType<CarsSpawner>().GameOver();
		isGameOver = true;
	}
}

}

Try checking for user input in Update() rather than FixedUpdate().

Does that make any difference?