Fasting c peptide level of 0.4 nmol/l is within normal which means u still have insulin producing capacity thats why u were able to control diabetes with oral medicines. But gad antibodies are positive so u r a case of LADA (Latent Autoimmune  diabetes of adults/adulthood). I'm afraid the mainstay of treatment in your case remains insulin though some beta cell sparing medicine may be used as adjunct.