This may help.
On a different topic, you are leaving yourself wide open to SQL injection attacks (do some research).
Consider what would happen if I typed this into the text box:
';DELETE FROM Stock_Entry;SELECT * FROM Stock_Entry where Item_Code='
Also, you are going back to the DB on every single key press i.e. item code 123456 requires 6 (slow) database calls, if you read 1% into local data and then queries this against 12%, 123% etc things may be a lot quicker.