Button click for movement

I have a UI button that triggers an event when it is clicked, and when it is released. The point of this is when I hit the "left" button, the player moves left. when it is released, the player stops. Same goes for the "right" button. I tried having a bool called righton and lefton, and then set these bools to true when the button is pressed, and false when released. This worked, and I could see in the console that the value was true when pressed, and false when released, which is what I wanted. However, if I tried sending the value in my FixedUpdate() the value was always false. Now I have the code below, that sets the SidewaysForce to 70, -70, or 0 based on if the buttons are pressed. I have a log statement that shows the value of SidewaysForce changing when I press or release the button. In the fixed update, I have it adding a force to my rigid body rb, but it is not working. any ideas?

 using UnityEngine;
 using UnityEngine.SceneManagement;
 using UnityEngine.EventSystems;
 using UnityEngine.Events;
 using UnityEngine.UI;
 using System.Collections;
 public class PlayerMovement : MonoBehaviour
 {
     //rigid body of my player
     public Rigidbody rb;
     //a constant forward force
     public float ForForce=4845f;
     //the force of the sideways movement, manually set to 70 outside of code
     public float SideForce=400f;
     //variable used to determine the sideways force
     public float SidewaysForce;
 
 
     public void Start()
     {
         rb.useGravity = true;
     }
 
     //this function happens when I click the button or release the button. Pushing the button sets lval to 1, releasing it sets the lval to 2
     public void LeftButton(int lval)
     {
         if (lval == 1) //button is pressed
         {
             //calls the move left function, and shows me in the console if i pushed the button, which works
             moveleft();
             Debug.Log("left");
         }
         else           //button is released
         {
             //calls the dont move left function, and shows when the button is released, which is working
             Debug.Log("not left");
             dontmoveleft();
         }
     }
 
     //sets the sideways force 
     public void moveleft()
     {
         SidewaysForce = SideForce;
         Debug.Log(SidewaysForce); //shows the sideways force = 70 when it is pressed
     }
 
     //removes the sideways force by setting it = 0
     public void dontmoveleft()
     {
         SidewaysForce = 0f;
         Debug.Log(SidewaysForce); //shows me that the force is = 0 when released
     }
 
     //same as move left, but opposite direction
     public void moveright()
     {
         SidewaysForce = -SideForce;
         Debug.Log(SidewaysForce); //shows the force = -70 when pressed
     }
 
     //same as dontmoveleft
     public void dontmoveright()
     {
         SidewaysForce = 0f;
         Debug.Log(SidewaysForce);
     }
 
     //same as leftbutton
     public void RightButton(int rval)
     {
         reval = rval;
         if (rval == 1)
         {
             moveright();
             Debug.Log("right");
         }
         else if (rval==2)
         {
             Debug.Log("not right");
             dontmoveright();
         }
     }
     private void OnDestroy()
     {
         FindObjectOfType<GameManager>().EndGame();
     }
    
 
 
     // Update is called once per frame
     void FixedUpdate()
     { 
     rb.AddForce(0, 0, ForForce * Time.deltaTime);     //constant forward force
     rb.AddForce(SidewaysForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);   //should add the sideways force but doesnt work
 
 
 
         //ignore the rest of this
         if (Input.GetKey("m"))
         {
             SceneManager.LoadScene("menu");
         }
         if (transform.position.y<-1)
         {
             FindObjectOfType<Lives>().EndGame();
             FindObjectOfType<GameManager>().EndGame();
         }
         if(transform==null)
         {
             FindObjectOfType<Lives>().EndGame();
             FindObjectOfType<GameManager>().EndGame();
         }
 
     }
 }