PHP and SQL authentication uses 100% of database capacity - php

Question

I've a webpage to a webinar with id 217, and to to verify if a user can watch the webinar, I use that function:
function user_verify($idlive, $register){
require("connect.php");
$query = "SELECT * FROM `users` WHERE idlive = 217 && register = '$register'";
$result = mysqli_query($conn, $query);
$user = mysqli_fetch_assoc($result);
mysqli_close($conn);
if(isset($user)){
return 1;
} else {
return 0;
}
}
If return 1, I call the function to access the webinar:
function login($register){
require("connect.php");
$data_hora_inscricao = date('d/m/y H:i:s');
$query = "SELECT * FROM `users` WHERE register = '$register' && idlive = 217";
$result = mysqli_query($conn, $query);
$user = mysqli_fetch_assoc($result);
mysqli_close($conn);
if(isset($user)){
$data = [
'u_id' => $user['id'],
'u_name' => $user['nome'],
'u_email' => $user['email'],
'u_level' => $user['level'],
'u_time' => 0
];
$dadosUserCookie = serialize($data);
setcookie('d_user_217', $dadosUserCookie, time() + (86400 * 1), "/");
return 1;
} else {
return 0;
}
}
If it returns 1 (success), I set a cookie to request user data on other pages. It always worked well, until yesterday. I don't know what's going on, but my AWS Lightsail database shows me that this code is using 100% of database capacity. What I can do to solve this?