Log in and run query based on a select value - php

Question

Im trying to use a select box to run different sql to log the user into my site. But for some reason it doesnt work. It "just shows the This user does not exist, please register first if you wish to continue message" that i have at the end.
My plan was just to get the value by using $_POST and storing it in a variable and then just say if that equals this then run this sql to change the value of $databpass and $databuser. (See code for more)
Also for some reason the first if statement works and i can log in. I tried else if but that was the same.
All Help Appreciated thx :D
Please bare in mind that i am fairly new to stackoverflow and php
$username = $_POST ['Username'];
$password = $_POST ['Password'];
$c= $_POST ['ch'];
if ($c=="S")
{
include 'connect.php';
$squery = mysql_query("SELECT * FROM S WHERE Username='$username'" );
$snumrow = mysql_num_rows($squery) or die(mysql_error());
if ($snumrow!=0)
{
while($row = mysql_fetch_assoc($squery)){
$databuser = $row['Username'];
$databpass = $row['Password'];
}
}
}
if ($c=="Or")
{
include 'connect.php';
$oquery = mysql_query("SELECT * FROM O WHERE Username='$username'" );
$onumrow = mysql_num_rows($oquery) or die(mysql_error());
if ($onumrow!=0)
{
while($row = mysql_fetch_assoc($oquery)){
$databuser = $row['Username'];
$databpass = $row['Password'];
}
}
}
if ($c== "C")
{
$query = mysql_query("SELECT * FROM C WHERE Username='$username'" );
$numrow = mysql_num_rows($query) or die(mysql_error());
if ($numrow!=0)
{
while($row = mysql_fetch_assoc($query)){
$databuser = $row['Username'];
$databpass = $row['Password'];
}
}
}
if ($username==$databuser&&$password==$databpass)
{
$_SESSION['username']=$username;
setCookie("sessionUsername", $username, time()+ 3600);
header("Location: memberprofile.php");
}
else
echo "Incorrect pass";
}
else
die("This user does not exist, please register first if you wish to continue");