PHP - Ayuda con este problema

<?php

//include("connect_db.php");

//$miconexion = new connect_db;

session_start();

  require("conexion.php");

  $username=$_POST['email'];

  $pass=$_POST['pass'];

  //la variable  $mysqli viene de connect_db que lo traigo con el require("connect_db.php");

  $sql2=mysqli_query($con,"SELECT * FROM clientes WHERE email='$username'");

  if($f2=mysqli_fetch_assoc($sql2)){

    if($pass==$f2['pasadmin']){

      $_SESSION['id']=$f2['id'];

      $_SESSION['nombre']=$f2['nombre'];

      echo '<script>alert("BIENVENIDO ADMINISTRADOR")</script> ';

      echo "<script>location.href='admin.php'</script>";

    }

  }

  $sql=mysqli_query($con,"SELECT * FROM clientes WHERE email='$username'");

  if($f=mysqli_fetch_assoc($sql)){

    if($pass==$f['password']){

      $_SESSION['id']=$f['id'];

      $_SESSION['nombre']=$f['nombre'];

      header("Location: index2.php");

    }else{

      echo '<script>alert("CONTRASEÑA INCORRECTA")</script> ';

      echo "<script>location.href='index.php'</script>";

    }

  }else{

  }

?>