How to Filter Database Records using Dropdown (PHP)

I want to filter database records using dropdown and display it in table but my code isn’t working which the data is not displayed. Here are my codes:

This the dropdown code:

<div class="cent3">
      <div class="form-group row">
        <div class="col-lg-4">
            <select name="month" class="form-control col-sm-12">
            <option>Select Expenses Month</option>
            <option value="January" style="color:black;">January</option>
            <option value="February" style="color:black;">February</option>
            <option value="March" style="color:black;">March</option>
            <option value="April" style="color:black;">April</option>
            <option value="May" style="color:black;">May</option>
            <option value="June" style="color:black;">June</option>
            <option value="July" style="color:black;">July</option>
            <option value="August" style="color:black;">August</option>
            <option value="September"style="color:black;">September</option>
            <option value="October"style="color:black;">October</option>
            <option value="November" style="color:black;">November</option>
            <option value="December" style="color:black;">December</option>
          </select>
          <input type="submit" name="submit" class="btn btn-primary">
      </div>
    </div>
    </div> 

And this code for data to be display in the table:

<div class="cent3">
      <div class="col-md-6">
        <table class="table table-hover table-bordered" >
                <tr>
                  <caption><p style="color:black;">Expenses by Month</p></caption>
                  <th><p style="color:black;">Month</p></th>
                  <th><p style="color:black;">Amount</p></th>
                  <th><p style="color:black;">Category</p></th>      
                </tr>
          <tr>
              <?php
                if(isset($_POST['submit'])){
                  $month = $_POST['MONTH(expenses_date)'];
                  $amount = $_POST['totalexp'];
                  $category = $_POST['expenses_category'];


                  if ($month != "" ) {
                    $query = "SELECT expenses_category, SUM(expenses_amount) as totalexp,MONTHNAME(expenses_date)as month 
                              FROM expenses 
                              WHERE MONTH(expenses_date) = '$month' AND user_id = '$user_id'
                              GROUP BY expenses_category";

                    $data = mysqli_query($con, $query) or die('error');
                    if(mysqli_num_rows($data) > 0){
                      while($row = mysqli_fetch_assoc($data)){
                        $month = $row['month'];
                        $amount = $row['totalexp'];
                        $category = $row['expenses_category'];

                      ?>
                      <tr>
                        <td><?php echo $month;?></td>
                        <td><?php echo $amount;?></td>
                        <td><?php echo $category;?></td>
                      </tr>
                      <?php 
                      }
                    }
                    else{
                        ?>
                        <tr>
                          <td>Records Not Found!</td>
                        </tr>
                        <?php
                        }
                    }

                }        
              ?>
        </table>
      </div> 
    </div>  

Currently, I’m using date picker for expenses_date input (format ‘Y-M-D’) but I want to display it in month name. So, the data in the table should display month, total amount in category and the category

I really appreciate your help. Thank you.