<?php
$TwoWeeksAgo = new DateTime(date("Ymd"));
$TwoWeeksAgo->sub(new DateInterval('P'.abs ( (7-date("N")-14)).'D'));
$LastWeek = new DateTime(date("Ymd"));
$LastWeek->sub(new DateInterval('P'.abs ( (7-date("N")-7)).'D'));
$ThisWeek = new DateTime(date("Ymd"));
$ThisWeek->add(new DateInterval('P'.abs ( (7-date("N"))).'D'));
echo 'Start of This week is '.$ThisWeek->format('m/d/Y').'<br/>';
echo 'Start of Last week is '.$LastWeek->format('l m/d/Y').'<br/>';
echo 'Start of 2 weeks ago is '.$TwoWeeksAgo->format('l m/d/Y').'<br/>';