I have a bit of a conundrum.  I recently upgraded a ~20gb database from WS2008r2xSQL2008r2
to WS2012xSQL2012.  The previous server had 32gb of memory, upon booting the Max Server memory of 28gb would be consumed within one day.  The new server has 48gb of memory however upon booting the database
 
  a) does not take the minimum memory of 4gb   
  b) after a week of running has only consumed 7gb of data

The database is mainly ad-hoc workload that does not utilize stored procs. So the hope in adding memory that was more of query plans would stay cached.  

Any idea what could be causing this ?

Thanks