storing session data to mysql tables and last_insert_id function - php

Question

When a nurse logs into the patient system, details about her are stored in session variables - including her user id. I have created a registration script so that when the nurse registers a new patient, her id is stored in the super column of the user table. This is so the patient can be allocated to her only.
The problem is that when I run the insert statement, the value 0 is stored in the super user column instead of the user id of the nurse. How can this be solved?
I have a profile table that has the profile of the user and it links to the user table. I have used the first insert statement to create the record in the user table. I want the second statement to create a record in the profile table with the profile id being the same as the newly created user_id. I am trying to use the LAST_INSERT_ID() function, but it too is storing 0 and not the last id.
Here is my code around the specific part in question. I am sorry if the formatting is not correct. I am using a screen reader and the formatting options on this website arn't very accessible to me.
I have stored the form data from $_post into all the variables used below.
$SuperUser = $_SESSION['SuperUser'];
//insert query for user table
$UserInsert = "insert into user
(User_id,
Username,
Password,
User_level,
SuperUser)
values(null,
'$Username',
'$Password',
'1',
'$SuperUser')";
//run query for inserting data for user table
mysql_query($UserInsert) or die("cannot insert into user");
//Select the last increment id from user table
$LastIdQuery = "Select LAST_INSERT_ID()";
$LastId = mysql_query($LastIdQuery) or die("Cannot select last id");
//insert query for profile table
$ProfileInsert = "insert into profile
(User_id,
FirstName,
LastName,
Dob,
NI_Number,
NHS_Number,
Address1,
Address2,
Town,
Postcode,
Email,
Contact_Number,
Comments)
values('$LastId',
'$FirstName',
'$LastName',
'$DobYear-$DobMonth-$DobDay',
'$NI_Number',
'$NHS_Number',
'$Address1',
'$Address2',
'$Town',
'$Postcode',
'$Email',
'$Contact_Number',
'$Comments')";
//insert into profile
mysql_query($ProfileInsert) or die("Unable to insert in profile");
mysql_close();

Answer 1

Try doing $id = mysql_insert_id() instead of the LAST_INSERT_ID function that you're doing. Also, if you're storing the mysql connection in a variable, passing it to mysql_insert_id() can make it more accurate. E.g when connecting to database:
$link = mysql_connect(......);
then later:
mysql_query($ProfileInsert) or die("Unable to insert in profile");
$id = mysql_insert_id( $link );
mysql_close( $link );