Use
$time = time();
For previous day -
date("Y-m-d", mktime(0,0,0,date("n", $time),date("j",$time)- 1 ,date("Y", $time)));
For 2 days ago
date("Y-m-d", mktime(0,0,0,date("n", $time),date("j",$time) -2 ,date("Y", $time)));
For Next day -
date("Y-m-d", mktime(0,0,0,date("n", $time),date("j",$time)+ 1 ,date("Y", $time)));
For next 2 days
date("Y-m-d", mktime(0,0,0,date("n", $time),date("j",$time) +2 ,date("Y", $time)));