Pygame Game Is Lagging when spawning enemies

I'm trying to make a pygame and I ran into a problem with enemy spawning.I was just testing it out of see if it would work but when the player would move the game would lag like here.Bear in mind that i'm in 6th grade and just started leaing pygame a week ago and python in April.Also when I try to run the program it's give the error that the variable 'xenemy' is not defined.I took that out when I ran the game but added in here because it is also a bug. Here is my code:

                                     import pygame,sys
import random
import time
from pygame.locals import *
pygame.init()

#WINDOW
WIDTH = 352
HEIGHT = 122
pygame.display.set_caption('My First Python Game')
screen=pygame.display.set_mode((WIDTH,HEIGHT))



#LOADING IMAGES
pg = "player.gif"
ey = "enemy.gif"
bg = "y.gif"
a = 0
enemypic = pygame.image.load(ey)
player = pygame.image.load(pg)
spriteWidth, spriteHeight = player.get_rect().size
background = pygame.image.load(bg)

#MUSIC
pygame.mixer.music.load("music.mp3")
pygame.mixer.music.play(-1,0.0)

#X & Y AXIS
x = 0
y = 0

#Enemy
def enemy():
 xenemy = random.randrange(24,147)
 yenemy = random.randrange(1,135)
 global  xenemy
 global  yenemy


 #Main Game Loop
 while True:
  for event in pygame.event.get():
    if event.type == QUIT:
     pygame.quit()
    sys.exit
    x = min(max(x, 0), WIDTH - spriteWidth)
    y = min(max(y, 0), HEIGHT - spriteHeight)
    screen.blit(background,[0,0])
    if event.type == pygame.KEYDOWN:
     if event.key == pygame.K_s:
      x  += 45
    screen.blit(enemypic, (xenemy,yenemy))
    screen.blit(player, (y,x))
    pygame.display.update()
    if x <= WIDTH:
      x = 0
    if y <= HEIGHT:
      y = 0
    if a == 0:
     pygame.display.flip()
     time.sleep(1)