How do I make things appear after an "if" statement in python?

This is my "game" that is about being a square, picking up the yellow "blips" and avoiding the blue enemies. My problem is that the enemies appear before the if statement, even though they shouldn't. I don't know if blitting is the best way of doing it, but since I am a beginner I do not know, and it's been working well for me so far. I also want to cover up or remove the "ball" but can't find a way to do that, since blitting in an "if" statement does not work and covers it immidiately. If there is any help or tips you can come with I will gladly accept, as well as how to improve and/or cleaning up my code. Thanks in advance!

import sys, pygame
from random import randint

pygame.init()

size = width, height = 800, 600
speed = [2, 2]
green = 0,255,0
black = 1, 1, 1
screen = pygame.display.set_mode((size))
pygame.display.set_caption('Pick up the squares!')
UP='up'
DOWN='down'
LEFT='left'
RIGHT='right'

ballx = 400
bally = 300
ballpos = (ballx, bally)
ball = pygame.image.load("ball.png")
ballrect = ball.get_rect(topleft = (ballx, bally))

endBlipx = 0
endBlipy = 0


blipx = randint(1,800)
blipy = randint(1,600)

blippos = (blipx, blipy)
blip = pygame.image.load("blip.png")
bliprect = blip.get_rect(topleft = (blipx, blipy))


enemy1x = randint(1,800)
enemy1y = randint(1,600)
enemy1pos = (enemy1x, enemy1y)
enemy1 = pygame.image.load("enemy.png")
enemy1rect = blip.get_rect(topleft = (enemy1x, enemy1y))

enemy2x = randint(1,800)
enemy2y = randint(1,600)
enemy2pos = (enemy2x, enemy2y)
enemy2 = pygame.image.load("enemy.png")
enemy2rect = blip.get_rect(topleft = (enemy2x, enemy2y))

enemy1changex = 5
enemy1changey = 5

enemy2changex = 5
enemy2changey = 5


newPosx = randint(1,795)
newPosy = randint(1,595)

background = pygame.Surface(screen.get_size())
background = background.convert()    
background.fill((250, 250, 250))



scoreNum = 0


font = pygame.font.Font(None, 36)
text = font.render("{}{}".format("Score: ", scoreNum),8,(250,0,0))
textpos = text.get_rect()
textpos.centerx = background.get_rect().centerx
background.blit(text, textpos)




clock = pygame.time.Clock()

while 1:
    for event in pygame.event.get():
        if event.type == pygame.QUIT: sys.exit()


    keys = pygame.key.get_pressed()

if keys[pygame.K_LEFT]:
    ballx  -= 5
    ballrect.x -=5
if keys[pygame.K_RIGHT]:
    ballx += 5
    ballrect.x += 5
if keys[pygame.K_UP]:
    bally -= 5
    ballrect.y -= 5
if keys[pygame.K_DOWN]:
    bally +=5
    ballrect.y += 5

if ballrect.colliderect(bliprect): 
    blipx = randint(1,795)
    blipy = randint(1,595)
    bliprect = blip.get_rect(topleft = (blipx, blipy))

    scoreNum = int(scoreNum)
    scoreNum = scoreNum + 1
    scoreNum = str(scoreNum)
    text = font.render("{}{}".format("Score: ", scoreNum),8,(250,0,0))
    scoreNum = int(scoreNum)


if ballx >= 765:
    ballx -= 5
    ballrect.x -= 5
if bally <= -5:
    bally += 5
    ballrect.y += 5
if ballx <=-5:
    ballx +=5
    ballrect.x +=5
if bally >=565:
    bally -=5
    ballrect.y -=5

if scoreNum >= 5:
    screen.blit(enemy1, (enemy1x, enemy1y))
    screen.blit(enemy1, (enemy1rect))

    enemy1x += enemy1changex
    enemy1y += enemy1changey
    enemy1rect.x += enemy1changex
    enemy1rect.y += enemy1changey

    if enemy1x > 795 or enemy1x < 5:
        enemy1changex = enemy1changex * -1
    if enemy1y > 595 or enemy1y < 5:
        enemy1changey = enemy1changey * -1

if scoreNum >= 6:

    screen.blit(enemy2, (enemy2x, enemy2y))
    screen.blit(enemy2, (enemy2rect))

    enemy2x += enemy2changex
    enemy2y += enemy2changey
    enemy2rect.x += enemy2changex
    enemy2rect.y += enemy2changey

    if enemy2x > 795 or enemy2x < 5:
        enemy2changex = enemy2changex *-1
    if enemy2y > 595 or enemy2y < 5:
        enemy2changey = enemy2changey * -1




if ballrect.colliderect(enemy1rect):
    screen.fill(black)
    pygame.draw.rect(screen, black, (ballrect.x, ballrect.y, 20, 20))
    text = font.render("{}".format("You lose!!"), 8, (250,0,0))
    scoreNum = 0

if ballrect.colliderect(enemy2rect):
    screen.fill(black)
    pygame.draw.rect(screen, black, (ballrect.x, ballrect.y, 20, 20))
    text = font.render("{}".format("You lose!!"), 8, (250,0,0))
    scoreNum = 0


if scoreNum == 6:
    text = font.render("{}".format("You win!"), 8, (250,0,0))






screen.fill(black)
screen.blit(ball,(ballrect))
screen.blit(ball, (ballx, bally))
screen.blit(blip,(bliprect))
screen.blit(blip, (blipx, blipy))
screen.blit(enemy1, (enemy1x, enemy1y))
screen.blit(enemy1, (enemy1rect))
screen.blit(enemy2, (enemy2x, enemy2y))
screen.blit(enemy2, (enemy2rect)) 
screen.blit(text, textpos)
pygame.display.update()
clock.tick(40)