It looks like you are using an array for the checkbox values. If you would like to see the values for the checkbox when it is an array like this you need to do some array manipulation.
The first thing that you should do is remove the brackets that are in the name of the posted element so it is like this:
php:
$_POST["fieldset_group_Check_any_infection_you_had_in_the_past"]
If you had it like this you would see array() for the value of the checkbox fields. You need to manipulate this array to see all of the values in it. The easiest way to do this would be to implode the array. It would look like this:
php:
<?php echo((isset($_POST["fieldset_group_Check_any_infection_you_had_in_the_past"]))?implode(", ", $_POST["fieldset_group_Check_any_infection_you_had_in_the_past"]):"") ?>
The implode function takes an array and a separator and makes a string of values separated by the separation characters you specify. Here is a link to the php page with more info:
php.net/implode
