Character jittering when moving and constant back and forth when colliding.

Hi,

I have this code for my 2D character movement along the x axis:

 if(Input.GetKey(KeyCode.RightArrow)){
             Vector3 position = new Vector3(this.transform.position.x,this.transform.position.y,this.transform.position.z);
             position.x = position.x + 0.2f;
             this.transform.position = position;
         }
 
         if(Input.GetKey(KeyCode.LeftArrow)){
             Vector3 position = new Vector3(this.transform.position.x,this.transform.position.y,this.transform.position.z);
             position.x = position.x - 0.2f;
             this.transform.position = position;
         }
 
         if(Input.GetKeyDown(KeyCode.Space)){
             if(!isJumping){
                 isJumping = true;
                 rigidbody2D.AddForce(new Vector2(0, 20), ForceMode2D.Impulse);
             }
         }

Works fine for movement, but it is jittery.

I tried using deltaTime to make it smooth, but for some reason it work well then while holding the right arrow, the player slows down after a few seconds.

When my player collides with an object and the arrow is still held down, it jumps back and forth.

What am i doing wrong here?

Thanks for your help in advance.