This is definately a very late reply but just incase some one googled and gets here.
Incase you(Shapam) are still in need of this,
First of, if you are tracking this yourself, you need to have an audit trail table. This table basically keeps records of all activities performed on various tables of your db. You should have a column that records the dates the changes were made.
This means that, you would need to write a query that inserts into the audit trail table everytime changes are made to all tables. Then you could always query the audit trail table.