multiple if statements, only one works [closed]

So I'm trying to create a restaurant menu that a user can choose an appetizer and an entree from through pygame rects and collisions. I have four if statements for four rectangles that will return a value that will then be used as an index to pull from a list. However, the program only functions with the first if statement and always returns a value of 0, even if I don't click the box and my mouse clicked on a different button. I've tried isolating the other if statements and also found that they did not return a value individually, and only the app_box_one functioned correctly when clicked. Clicking on app_box_two or the other boxes did not do anything and kept the value of a = None. I also read about return ending the function, but I'm not sure if that is the problem here as all the other boxes (even though they are the exact same, just a lower y coordinate) other than app_box_one don't do anything. Sorry this is a long question, any help is appreciated.

def main():
a = None
e = None
run = True
FPS = 60
while run:
    window.fill(WHITE)
    window.blit(menu, (0, 0))
    clock = pygame.time.Clock()
    clock.tick(FPS)
    app_box = pygame.Rect(WIDTH / 2 - 215, HEIGHT / 2 - 200, 200, 75)
    entree_box = pygame.Rect(WIDTH / 2 + 30, HEIGHT / 2 - 200, 200, 75)
    pos = pygame.mouse.get_pos()
    if app_box.collidepoint(pos):
        if clicking:
            a = screen(1, 0)
            print(a)
    if entree_box.collidepoint(pos):
        if clicking:
            e = screen(0, 1)
    pygame.draw.rect(window, NUTMEG, app_box)
    pygame.draw.rect(window, NUTMEG, entree_box)
    draw_win()
    clicking = False
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
            pygame.quit()
        if event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:
                clicking = True
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE:
                pygame.quit()
    if a != None and e != None:
        meal(a, e)
    pygame.display.update()


def screen(app, ent):
    mx, my = pygame.mouse.get_pos()
    if app == 1:
        running = True
        while running:
            window.fill(WHITE)
            window.blit(menu, (0, 0))
            app_box_one = pygame.Rect(WIDTH/3 - 100, HEIGHT/5, 400, 100)
            pygame.draw.rect(window, NUTMEG, app_box_one)
            app_box_two = pygame.Rect(WIDTH/3 - 100, HEIGHT/3 + 45, 400, 100)
            pygame.draw.rect(window, NUTMEG, app_box_two)
            app_box_three = pygame.Rect(WIDTH/3 - 100, HEIGHT - 350, 400, 100)
            pygame.draw.rect(window, NUTMEG, app_box_three)
            app_box_four = pygame.Rect(WIDTH/3 - 100, HEIGHT - 200, 400, 100)
            pygame.draw.rect(window, NUTMEG, app_box_four)
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    pygame.quit()
                if event.type == pygame.MOUSEBUTTONDOWN:
                    if app_box_one.collidepoint(mx, my):
                        app_ix = 0
                        return app_ix
                    if app_box_two.collidepoint(mx, my):
                        app_ix = 1
                        return app_ix
                    if app_box_two.collidepoint(mx, my):
                        app_ix = 2
                        return app_ix
                    if app_box_two.collidepoint(mx, my):
                        app_ix = 3
                        return app_ix
                if event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_ESCAPE:
                        running = False

            pygame.display.update()
            main_clock.tick(60)
    if ent == 1:
        running = True
        while running:
            window.fill(WHITE)
            window.blit(menu, (0, 0))
            option_box_one = pygame.Rect(WIDTH/3 - 100, HEIGHT/5, 400, 100)
            pygame.draw.rect(window, NUTMEG, option_box_one)

            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    pygame.quit()
                if event.type == pygame.MOUSEBUTTONDOWN:
                    if option_box_one.collidepoint(mx, my):
                        entree_ix = 0
                        return entree_ix
                if event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_ESCAPE:
                        running = False

            pygame.display.update()
            main_clock.tick(60)

def meal(app_index, entree_index):
    window.fill(WHITE)
    window.blit(menu, (0, 0))
    meal_font_one = pygame.font.SysFont('corbel', 35, True, True)
    meal_font_two = pygame.font.SysFont('corbel', 35, True, True)
    meal_message_one = app_list[app_index]
    meal_message_two = entree_list[entree_index]
    final_meal_message_one = meal_font_one.render(meal_message_one, True, BLACK)
    window.blit(final_meal_message_one, (WIDTH/4 - 120, HEIGHT/2))
    final_meal_message_two = meal_font_two.render(meal_message_two, True, BLACK)
    window.blit(final_meal_message_two, (WIDTH / 4 - 120, HEIGHT / 2 - 50))
    pygame.display.update

main()