If he tested your c-peptide when your blood sugar was very high (any idea what it was at the time), the c-peptide may appear 'normal', because your poor pancreas was sputtering as hard as it could to put out insulin.
Your presentation sounds very much like type 1 (or Lada). Your gestational history, also makes type 1 more likely. THe fact you have antibodies is a clear giveaway for Autoimmune type diabetes. The fact that your a1c was 12.6 is also an alarm. From what I have read, even in type 2, if a1c is that high, then you should be on insulin (each medication is only expected to reduce a1c by about 1%, if I remember what I read correctly). IF you were type 2, then a combo of 4 drugs might bring you down to about 8.0. Still not ok.
Glipizide is not a good drug. It forces your pancreas to put out more insulin (too bad if it can't). My only advice echoes everyone else's. Change Drs. Go back to your GP and get back on insulin. Find an endo who will treat you properly. You may or may not need an insulin sensitizer as well (such as metformin).