Repaint() isn't working an I don't know why

public static void main(String[] args){
    Core game = new Core();
    game.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    game.frame.setTitle("Multiply");
    game.frame.setIconImage(testIcon);
    game.frame.add(game);
    game.frame.pack();
    game.frame.setLocationRelativeTo(null);
    game.frame.setResizable(false);
    game.frame.setVisible(true);

    t1.start();

    new Core().run();
}

public Core(){
    KeyListener listener = new MyKeyListener();
    addKeyListener(listener);
    setFocusable(true);

    Dimension size = new Dimension(width, height);  //variable that sets the size of the window to 1280x720p
    setPreferredSize(size);                         //Sets the size of the window to "size" 

    frame = new JFrame();                           //makes frame into the JFrame window
}


public void run(){
    running = true;
    loop();
}

public void render(){
        repaint();
        System.out.println("runnin");
}

private synchronized void loop(){   //Running loop, while the game is open this will always be running
    long lastLoopTime = System.nanoTime();
    final int TARGET_FPS = 60;
    final long OPTIMAL_TIME = 1000000000 / TARGET_FPS;
    int fps = 0;
    long lastFpsTime = 0;

    while(running == true){
        long now = System.nanoTime();
        long updateLength = now - lastLoopTime;
        lastLoopTime = now;
        double delta = updateLength / ((double)OPTIMAL_TIME);

        lastFpsTime += updateLength;
        fps++;

        if (lastFpsTime >= 1000000000)
          {
             System.out.println("(FPS: "+fps+")");
             lastFpsTime = 0;
             fps = 0;
          }

        enemyAI();
        render();

        try {
            Thread.sleep( (lastLoopTime-System.nanoTime() + OPTIMAL_TIME)/1000000 );
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public void enemyAI(){
    if(menu != true){
        enemyX++;
    }
}

@Override
public synchronized void paint(Graphics g) {        // Draws top first to bottom last 
    super.paint(g);
    String imagesString = "C:/Users/BigBertha/Desktop/Multiply_Game_Engine/";
    Image background = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/Green_Background.png");
    Image character = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/Character.png");
    Image enemy = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/Enemy.png");
    Image inDevText = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/InDevText.png");

    Image menuScreen = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/MainMenu.png");
    Image menuArrow = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/MainMenuArrow.png");
    //Image loadingScreen = Toolkit.getDefaultToolkit().getImage(imagesString+"Images/LoadingScreen.png");

    if(menu){
        g.drawImage(menuScreen, 0, 0, 1290, 730, this);

        if(menuAPos1){ //play
            g.drawImage(menuArrow, menuArrowX1, menuArrowY1, 125, 100, this);
            loading = true;
        }
        else if(menuAPos2){
            g.drawImage(menuArrow, menuArrowX2, menuArrowY2, 125, 100, this);
        }
        else if(menuAPos3){
            g.drawImage(menuArrow, menuArrowX3, menuArrowY3, 125, 100, this);
        }
            g.drawImage(inDevText, width - 95, height - 20, 100, 40, this); //removed eventually
    }
else if(running){
        g.drawImage(background, 0, 0, 1290, 730, this); //draws the black background
        g.drawImage(inDevText, width - 95, height - 20, 100, 40, this); //removed eventually
        g.drawImage(character, charX, charY, charSizeX, charSizeY, this); //draws the character
        g.drawImage(enemy, enemyX, enemyY, enemySizeX, enemySizeY, this);
}
}

I need the loop() method to be able to run repaint() but it does nothing when it's called. I've tried many different variations to try and get it to work but nothing has worked. I've been thinking about using JOGL but i need to complete at least a decent amount of a game prototype for school.