ขอผู้รู้ช่วยดูให้หน่อยครับ ทำใมผมกดเปลี่ยนเดือนไม่ได้

<center><form action="add2.php" method="POST" enctype="multipart/form-date">
<table>
	<tr>
		<td align="right"><b><span style='color:#0000FF;'>นัดวันรับสิงค้า :</span></b></td>

		<style type="text/css">
		<!--
		body { margin: 0px 0px; padding: 0px 0px}
		a:link { color: #005CA2; text-decoration: none}
		a:visited { color: #005CA2; text-decoration: none}
		a:active { color: #0099FF; text-decoration: underline}
		a:hover { color: #0099FF; text-decoration: underline}
		-->
		</style>
			<td><div align="lift"><font color="#0000FF" style="font-family:sans-serif" size="+6">
			<?
			$a= date(j); // , 1 to 31 
			$b = date(a); // am,
			$c = date(A); // AM,
			$d = date(B); // Swatch Internet time 000 -999
			$e = date(d); // , 01 to 31
			$f = date(D); // , sat 
			$g = date(F); // , November 
			$h = date(g); // , 1 through 12
			$hh = date(G); // , 0 through 23
			$i = date(h); // , 01 through 12 
			$j = date(H); // , 00 through 23 
			$k = date(i); // , 00 to 59 
			$l = date(I); // 0, 1 if Daylight Savings Time, 0 otherwise. 
			$m = date(l); // , Sunday through Saturday
			$n = date(L); // 0, 1 if it is a leap year, 0 otherwise.
			$o = date(m); // , 01 through 12
			$p = date(M); // , Jan through Dec
			$q = date(n); // , 1 through 12
			$r = date(o); // Example: +0200 
			$s = date(r); // Example: Thu, 21 Dec 2000 16:01:07 +0200
			$t = date(s); // 00 through 59
			$u = date(S); // st, nd, rd or th. Works well with j 
			$v = date(t); // 28 through 31
			$w = date(T); // time zoneseting Examples: EST, MDT ...
			$x = date(u); // See also time()
			$y = date(w); // 0 (for Sunday) through 6 (for Saturday)
			$z = date(W); // Example: 42 (the 42nd week in the year)
			$aa = date(y); // Examples: 99 or 03
			$bb = date(Y); // Examples: 1999 or 2003
			$cc = date(z); 
			$dd = date(Z); 

			if(!$mon){
				$mon = $o ;
			}else{
				$mon = $mon ;
			}

			if(!$year){
				$year = $bb ;
			}else{
				$year = $year;
			}
			$firstday = mktime(0,0,0,$mon,1,$bb);
			$firstdays = date('w',$firstday); 
			$lastdays = date('t',$firstday); 
			$year_view = date('Y',$firstday); 
			$mon_view = date('m',$firstday);
			$thaimon=array("","มค.","กพ.","มีค.","เมย.","พค.","มิย.","กค.","สค.","กย.","ตค.", "พย.","ธค.");
			$thai_mon=$thaimon[$mon_view];

			echo"
			<script>
			function d_s( su , mnp){ 
			if(mnp=='n'){
				document.dat_form.mon.value=su-1;
			}else{
				document.dat_form.mon.value=su+1;
			}
			document.dat_form.submit();
			}
			</script>
			<form name=dat_form action='$PHP_SELF' method=post>
			<input type=hidden name=mon value=''>

			<table border=1 width=200 cellpadding=0 cellspacing=0 bordercolor=#999999>
				<tr bgcolor=pink>
					<td colspan=7 align=center><a href=\"javascript:d_s($mon,'n')\"> << </a>&nbsp;$thai_mon $year_view <a href=\"javascript:d_s($mon,'m')\"> >> </a>
					</td>
				</tr>
			</form>
				<tr align=center>
					<td><center><font color=red>อา</a></td><td>จ</td><td>อ</td><td>พ</td><td>พฤ</td><td>ศ</td><td><font color=blue>ส</font></td></center>
				</tr>
				<tr align=right>";
//// 
				for($i = 0; $i < 7 ; $i++){
				if($firstdays == $i){
					break;
				}else{
					echo"<td width=8>&nbsp;</td>";
				}
				$week++; 
				}

				for($i=1; $i<=$lastdays ;$i++){
				if($week % 7 == 0){
					echo"</tr><tr align=right>";
				}
				if($a == $i){ 
					$bgcolor = "bgcolor=pink";
				}else{
				$bgcolor = '';
				} 

				if($week%7==0){ 
					echo"<td $bgcolor><center><font size=2 color=red><a href=\"add.php?date_n=$i/$mon_view/$year_view\">$i</a></font></center></td>";
				}else if($week%7==6){ 
					echo"<td $bgcolor><center><font size=2 color=blue><a href=\"add.php?date_n=$i/$mon_view/$year_view\">$i</a></font></center></td>";
				}else{ // 
					echo"<td $bgcolor><center><font size=2><a href=\"add.php?date_n=$i/$mon_view/$year_view\">$i</a></font></center></td>";
				}
				$week++;
				}

				while($week%7!=0){
					echo"<td>&nbsp;</td>";
					$week++;
				}
				echo"</tr></table>";
			?>
		</td>
	</tr>
	<tr>
		<td align="right"><b><span style='color:#0000FF;'>ชื่อ - นามสกุล :</span></b></td>
		<td><input name="ืname" type="text" size="30"></td>
	</tr>
	<tr>
		<td align="right"><b><span style='color:#0000FF;'>หมายเลขบัตรประชาชน :</span></b></td>
		<td><input name="post" type="text" size="13" maxlength="13"></td>
	</tr>
	<tr>
		<td align="right"><b><span style='color:#0000FF;'>เบอร์โทรศัพท์ :</span></b></td>
		<td><input name="tel" type="text" size="10" maxlength="10"></td>
	</tr>
	<tr>
		<td align="right" valign="top"><b><span style='color:#0000FF;'>ที่อยู่ ติดต่อ :</span></b></td>
		<td><textarea name="address" cols="50" rows="5"></textarea></td>
	</tr>
	<tr>
		<td align="right" valign="top"><b><span style='color:#0000FF;'>อาการ :</span></b></td>
		<td><textarea name="title" cols="50" rows="5"></textarea></td>
	</tr>
	<tr>
		<td align="right" valign="top"><b><span style='color:#0000FF;'>วันนัด :</span></b></td>

		<td><input name="post" type="text" size="7" value="<? echo $date_n; ?>" disabled="disabled" readonly="readonly"></td>
	</tr>
	<tr>
		<td>&nbsp;</td>
		<td><input type="submit" value="บันทึกรายงาน"><input type="reset" value="ล้างออก"></td>
	</tr>
</table>
</form></center>

script>
			function d_s( su , mnp){ 
			if(mnp=='n'){
				document.dat_form.mon.value=su-1;
			}else{
				document.dat_form.mon.value=su+1;
			}
			document.dat_form.submit();
			}
			</script>