小弟我的分页，但是有异常，帮忙看看

我的分页，但是有错误，帮忙看看
这是我写的分页。但是有错误哦，比如我点末页后再点上一页，她还是在这一页，我点了首页再点下一页之后也是这个情况，求教！

$sql = "select * from pl_transaction_sun";
$query = mysql_query($sql);
$num = mysql_num_rows($query);

$pagesize = 3;
$start = $_GET['start'];
$flag = $_GET['flag'];

//判断$start是否有值
if ($start == null) {
$start = 0;
}

//判断$flag是否有值
if ($flag == null) {
$flag = 0;
}

$sql1 = "select * from pl_transaction_sun limit $start, $pagesize";
$query1 = mysql_query($sql1);
//$num1 = mysql_num_rows($query1);

//判断标志位以确定$start的值
if ($flag == 1 and $start+$pagesize $start = $start+$pagesize;
}
if ($flag == 2 and $start+$pagesize > 0){
$start = $start-$pagesize;
}

//最后一页START标识
if (($num % $pagesize) != 0){
$lastpage = $num - ($num % $pagesize);
}else{
$lastpage = $num - $pagesize;
}

//判断页数以及当前页代码
$pagenum = ceil($num / $pagesize);

if ($start == 0){
$nowpage = 1;
}else{
$nowpage = ($start / $pagesize) + 1;
}
print ("