PHP MySQLi - 传递图像不起作用

I'm trying to create an edit profile image where the user can edit stored profile, such as name, email etc, and also, update profile picture. However, whenever I try to upload a picture, while it exists in print_r I always get the "image empty" echo.

My code is this:

    $fname = $lname = $email = $userPw = $title = $link = $description = $target_file = "";
    $fnameError = $lnameError = $emailError = $pwError = $linkError =  $descError = $uploadErr = "";
    if ($_SERVER["REQUEST_METHOD"] == "POST") 
    {
        if(isset($_FILES["fileToUpload"]))
        {
            include ('../config/imageCheck.php');
            echo 'image is not empty';
        }
        else
        {
            echo 'image empty';
        }
        //rest of the code checks and db query

imageCheck is:

$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$imageFileType = pathinfo($target_file,PATHINFO_EXTENSION);

$check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
if($check == false)
{
    echo $uploadErr = "File is not an image.";
}

if (file_exists($target_file))
{
    echo $uploadErr = "File already exists.";
}

if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg" && $imageFileType != "gif" )
{
    echo $uploadErr = "Only JPG, JPEG, PNG & GIF files are allowed.";
}

if ($_FILES["fileToUpload"]["size"] > 200000)
{
    echo $uploadErr = "Your file is too large.";
}

and the form:

<form method="post" action=<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>>
   <input type="text" class="form-control" name="fname" id="fname" value="<?php echo $fname;?>" onkeyup="validateLetter(this.id)" placeholder="Enter First Name" required autofocus><span class="error"><?php echo $fnameError;?></span>
   <input type="text" class="form-control" name="lname" id="lname" value="<?php echo $lname;?>" onkeyup="validateLetter(this.id)" placeholder="Enter Last Name" required>
   <input type="file" class="form-control" name="fileToUpload" id="fileToUpload">
   <input type="submit" class="btn btn-primary" value="Sumbit">
</form>

If I change

if(isset($_FILES["fileToUpload"])

to

if(isset($_POST["fileToUpload"])

then I do get the "image is not empty echo" but imageCheck fails greatly, saying that

Notice: Undefined index: fileToUpload in C:\xampp\htdocs\ResearchWebsite\config\imageCheck.php on line 4

Notice: Undefined index: fileToUpload in C:\xampp\htdocs\ResearchWebsite\config\imageCheck.php on line 7

Warning: getimagesize(): Filename cannot be empty in C:\xampp\htdocs\ResearchWebsite\config\imageCheck.php on line 7 C:\xampp\htdocs\ResearchWebsite\config\imageCheck.php on line 27

Any help would be greatly appreciated! I'm at the brink of throwing my pc out of the window!