database - PHP laravel query -

how can query users last donation more 90 days. query when executed error unknown column.

      $value = session::get('key');       $datetoday = new datetime();       $data = users::where('usertype','=', 'user' )                 ->where($datetoday->format('m/d/y') - 'lastdonation', '=', 1)                 ->wherenotin('username', [$value ])                 ->get(); 

$data = users::where('usertype','=', 'user' ) ->where('lastdonation', '<', carbon::now()->subdays(90)) ->wherenotin('username', [$value ]) ->get();