Moving 2D Game Object on GUI Button Click

Hey guys, I need to move an object to the left when a button is clicked, changing the scene when it goes past a certain point. I want it to move steadily in a direction though instead of teleporting like it is now. Currently when I push the button my 2D player sprite just moves a few units to the right

void OnMouseDown(){
		Debug.Log("Pushed");
		if(currMenu == menuState.title)
		{
			currMenu = menuState.weapon;
		}
		else if(currMenu == menuState.weapon){

			objToMove.rigidbody2D.AddForce(Vector3.right * 3000);
			if (objToMove.transform.position.x > 15){
			Application.LoadLevel("Level1");
			}
		}
	}

OnMouseDown is only called once when you click. Use OnMouseOver which is called while your mouse is over the button. You can then check if the left mouse button is down and if so move your object. Something like this:

void OnMouseOver(){
	if(Input.GetMouseButton(0)){
		// move the player
	}
}

OnMouseOver will resolve this issue for you, Mike is correct.

void OnMouseOver(){
  if(Input.GetMouseButton(0)){
    if(currMenu == menuState.title)
    {
      currMenu = menuState.weapon;
    }
    else if(currMenu == menuState.weapon){
      objToMove.rigidbody2D.AddForce(Vector3.right * 3000);
      
      if (objToMove.transform.position.x > 15){
        Application.LoadLevel("Level1");
      }
    }
  }
}