On an average the oral anti diabetics are effective in controlling blood glucose
for about five years,during which period their effect gradually diminishes and ultimately a stage is reached when they are ineffective in controlling blood glucose even at the highest dose.
This stage is called as secondary SU failure or failure of beta cells in pancreas
to respond.As the time passes the mass of functionally active beta cells gradually diminishes and in about five years time a stage of secondary failure is reached.
I would advise you to consult a endocrinologist
and explore the use of more recently introduced medicines like GLIPTINS.
But ultimately,you may have to start injectable insulin
,once it is found that no oral anti diabetic is proving to be effective.