Jumping on enemies help

I'm trying to make a platformer with no jumping except for landing on enemies heads. It currently works but the jumping is sorta broken: if I am moving when I hit an enemy, the player will sometimes jump really low, sometimes a medium height, and sometimes really really high. See this gif for an example.

How can I make it more consistent? Here's the script I'm using for my Player, there is a blank GameObject as a child which I check for the ground layer with:

using System.Collections; using UnityEngine.SceneManagement;

public class Player : MonoBehaviour {

 [HideInInspector] public bool jump = false;   //used later for jump detect
 public float Speed = 365f;                //controls speed of player
 public float jumpForce = 1000f;       //controls how forceful jumps are
 public Transform groundCheck;      //gameobj thats used later for checking if touching ground


 private bool grounded = false;    //used for groundcheck
 private Rigidbody2D rb2d;    //name for rigidbody2d attached, used later for physics stuffs
 private SpriteRenderer spriteRenderer;  //renderer attached
 //Animator Animator;  //used to control animations!


 void Start ()
 {
     //Animator = GetComponent<Animator> ();  //calls an Animator component called Animator

 }
 // Use this for initialization
 void Awake () 
 {
     rb2d = GetComponent<Rigidbody2D>();   //calls rigidbody2d component called rb2d
     //Animator = gameObject.GetComponent<Animator>(); //calls an Animator component called Animator


 }

 // Update is called once per frame
 void Update () 
 {
     grounded = Physics2D.Linecast(transform.position, groundCheck.position, 1 << LayerMask.NameToLayer("Enemy")); //defines what grounded is: a gameobj that casts a line at its current pos that checks if the player is touching a layer called "Ground", what my floor is made out of. 

     if (grounded)  //can only jump if grounded is true, basically if is touching floor
     {
         jump = true;
     }
     if (Input.GetKey (KeyCode.R))
         SceneManager.LoadScene (SceneManager.GetActiveScene ().buildIndex - 0);
 }

     



 void FixedUpdate()
 {
     float Dirx = Input.GetAxis ("Horizontal") * Speed * Time.deltaTime;  //dirx is left or right depending on what on the x axis is pressed, a or left for left, and d or right for right. 
     transform.position = new Vector2 (transform.position.x + Dirx, transform.position.y);  //this transforms (moves) the player in the dir specified by dirx, and takes the speed from dirx too. 


     if (jump)
     {
         rb2d.AddForce(new Vector2(0f, jumpForce)); //adds a force to the rigidbody, multiplied by jumpforce.
         jump = false;  //can't jump right after jumping, until touching floor again. 
     }

} }

Any ideas? I'm new to unity, any help would be great, thanks!