How to create smooth object rotation in a WASD system?

I am trying to create a control scheme wherein the player controlled element can be rotated by the player using the WASD keys, but am having trouble creating a programmed scheme that doesn't stutter constantly or just barely move at all before returning to where it started. I need a system that rotates relative to the current rotation of the object, but also maintains rotation after each iteration of the code, or just a simpler coding solution.

This is my current code:

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

 public class PlayerControl : MonoBehaviour
 {
 
     public bool isMovingX;
     public bool isMovingY;
 
     public float movementX;
     public float movementY;
 
     public Quaternion rotationX1;
     public Quaternion rotationX2;
     public Quaternion rotationY1;
     public Quaternion rotationY2;
 
     private float timeCountX;
     private float timeCountY;
 
     void Start()
     {
         movementX = 3;
         movementY = 3;
 
         timeCountX = 3f;
         timeCountY = 3f;
     }
 
     void FixedUpdate()
     {
         if (Input.GetKey(KeyCode.W) == true && Input.GetKey(KeyCode.S) == false && isMovingX == false)
         {
             timeCountX = movementX * Time.deltaTime;
             rotationX1 = transform.rotation;
             rotationX2 = Quaternion.Euler(transform.rotation.X - 5, transform.rotation.y + 0, transform.rotation.z + 0);
             transform.localRotation = Quaternion.Slerp(rotationX1, rotationX2, timeCountX);
             isMovingX = true;
             StartCoroutine(WaitTimeX());
         }
         if (Input.GetKey(KeyCode.A) == true && Input.GetKey(KeyCode.D) == false && isMovingY == false)
         {
             timeCountY = movementY * Time.deltaTime;
             rotationY1 = Quaternion.Euler(transform.rotation.X, transform.rotation.Y, transform.rotation.Z);
             rotationY2 = Quaternion.Euler(transform.rotation.X + 0, transform.rotation.y - 5, transform.rotation.z + 0);
             transform.localRotation = Quaternion.Slerp(rotationY1, rotationY2, timeCountY);
             isMovingY = true;
             StartCoroutine(WaitTimeY());
         }
         if (Input.GetKey(KeyCode.S) == true && Input.GetKey(KeyCode.W) == false && isMovingX == false)
         {
             timeCountX = movementX * Time.deltaTime;
             rotationX1 = Quaternion.Euler(transform.rotation.X, transform.rotation.Y, transform.rotation.Z);
             rotationX2 = Quaternion.Euler(transform.rotation.X + 5, transform.rotation.y + 0, transform.rotation.z + 0);
             transform.localRotation = Quaternion.Slerp(rotationX1, rotationX2, timeCountX);
             isMovingX = true;
             StartCoroutine(WaitTimeX());
         }
         if (Input.GetKey(KeyCode.D) == true && Input.GetKey(KeyCode.A) == false && isMovingY == false)
         {
             timeCountY = movementY * Time.deltaTime;
             rotationY1 = Quaternion.Euler(transform.rotation.X, transform.rotation.Y, transform.rotation.Z);
             rotationY2 = Quaternion.Euler(transform.rotation.X + 0, transform.rotation.y + 5, transform.rotation.z + 0);
             transform.localRotation = Quaternion.Slerp(rotationY1, rotationY2, timeCountY);
             isMovingY = true;
             StartCoroutine(WaitTimeY());
         }
         if (Input.GetKey(KeyCode.W) == false && Input.GetKey(KeyCode.S) == false)
         {
             movementX = 5;
         }
         if (Input.GetKey(KeyCode.A) == false && Input.GetKey(KeyCode.D) == false)
         {
             movementY = 5;
         }
     }
 
     public IEnumerator WaitTimeX()
     {
         yield return new WaitForSeconds(0.1f);
         if (movementX > 1)
         {
             movementX = movementX - 0.5f;
         }
         isMovingX = false;
     }
 
     public IEnumerator WaitTimeY()
     {
         yield return new WaitForSeconds(0.1f);
         if (movementY > 1)
         {
             movementY = movementY - 0.5f;
         }
         isMovingY = false;
     }
 }