rigidbody2D Addforce Problem

Hello,

I am currently stuck. I wanted to create a thruster effect with two forces applied to an object. I have two empty gameobjects attached as a child on the bottom right and left side of the parent (the player). When I press 'a' the wrong (right) side goes up, pressing 'd' does nothing most of the time. I am confused.

If someone can help me out, I'd appreciate it. Thanks.

Here is the script:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class movement : MonoBehaviour 
 {
 
     public float speed = 20f;
     public int startingEnergy = 100;
     private float currentEnergy;
     public float energyFill = 10f;
     public float energyConsumption = 40f;
 
     public Slider energySlider;
     public GameObject leftThruster;
     public GameObject rightThruster;
 
 
     void Awake()
     {
         currentEnergy = startingEnergy;
     }
 
 
 
     void FixedUpdate () 
     {
         
 
         if (Input.GetKey ("d") && currentEnergy >= 0f) 
         {
             rigidbody2D.AddForceAtPosition(rightThruster.transform.position, transform.up * speed);
             currentEnergy -= energyConsumption * Time.deltaTime;
             energySlider.value = currentEnergy;
         }  
 
         else if (Input.GetKey ("a") && currentEnergy >= 0f) 
         {
             rigidbody2D.AddForceAtPosition(leftThruster.transform.position, transform.up * speed);
             currentEnergy -= energyConsumption * Time.deltaTime;
             energySlider.value = currentEnergy;
         }
         
         else 
         {
             if(currentEnergy <= 100f) 
             {
                 currentEnergy += energyFill * Time.deltaTime;
                 energySlider.value = currentEnergy;
             }
         }
     }
 }