The code could use some cleaning up to become more readable but if you add

use strict;
use warnings;
[download]

to help you spot and fix typos like

    if($apspath =~ /$previousmonthzip/) {

then perhaps the program would do what you expect?

Update: Well, most of the time, anyway. The method you're using to calculate yesterday's date and last month's date will work properly about 90% of the time and then fail on every 1st day of each month, every last day of half the months, and always in january. And perhaps on the last few days in March. If that's going to be a problem, you might want to look for a suitable Date module :-)