How to display current month and three posts from previous month?

What I am looking to do is display all entries minus one category from the current month (which I already have code in place for)+ three entries from the previous month. I want to be able to do this because I sometimes don’t post for a few days and would like to not have a blank home page because I don’t post until the 3rd or 4th of the month! I currently have the below snippet for showing he current month only and excluding the one category as described above!

$current_month = date('m');
$current_year = date('Y');
query_posts("cat=-1545&year=$current_year&monthnum=$current_month&order=DESC");

Any help would be appreciated!