You're recreating the sprites and textures every frame, including reloading the textures from files. You should do that once at the beginning of main() and then leave them alone in the game loop until you have a reason to change them (ie, when the player shoots you'll make a new sprite for that bullet, but it can use the existing bullet texture).
Also, global variables are bad. Move them all into main(). And try to indent more consistently so your code is easier to read.