You can create an array with months names.
Then use
date ('n') ... to get current month number
$mon[1] = 'Jan'
$mon[2] = 'Feb'
<?php
$mon = array(NULL, 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
$current = date('n');
echo 'current= ' . $mon[$current];
echo '<br />';
echo 'prev= ' . $mon[$current-1];