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 ("