Having a problem with wp_redirect in my plugin

In my plugin, I am getting an error with wp_redirect.

Here is my code:

public function update($year, $edit_id, $column1, $column2) {

		global $wpdb;

		$table_name = $wpdb->prefix . 'tableName_'.$year;

		$Column1 = intval($column1);

		$Column2 = intval($column2);

		$NewTotal = ($Column1 + $Column2);

		$wpdb->update($table_name, array('Column1' => $Column1, 'Column2' => $Column2, 'Column3' => $NewTotal), array('month_id' => $edit_id));

		wp_redirect(get_option('siteurl').'/wp-admin/admin.php?page=my-plugin');

		exit();

	}

I know that the code is working until I get to wp_redirect.

I get the following error

Warning: Cannot modify header information – headers already sent by (output started at /home/…/public_html/wp-admin/includes/template.php:1953) in /home/…/public_html/wp-includes/pluggable.php on line 1171

Any help would be greatly appreciated