How to make a word from the given characters and not duplicated words?

I want to make a word contain 3 characters only and no words duplicated

import requests, random
from colorama import Fore

while True:
    
    usr = ""

    for charachter in random.choices("abcdefghijklmnopqrstvwxyz1234567890"):
        user = usr+ charachter

    response = requests.get(f"https://www.instagram.com/{user}/")

    if (response.status_code == 200):
        print(Fore.RED + "Taken: " + Fore.BLUE + user)
    elif(response.status_code == 400):
        print(Fore.GREEN + "Avilable User: "+ Fore.BLUE +user)

>Solution :

try this:

import requests, random
from colorama import Fore

while True:
    usr = ""
    for i in range(3):
        while True:
            charachter = random.choices("abcdefghijklmnopqrstvwxyz1234567890")
            if str(charachter[-1]) not in usr:
                usr += str(charachter[-1])
                break

    response = requests.get(f"https://www.instagram.com/{usr}/")

    if (response.status_code == 200):
        print(Fore.RED + "Taken: " + Fore.BLUE + usr)
    elif(response.status_code == 400):
        print(Fore.GREEN + "Avilable User: "+ Fore.BLUE +usr)