If you were not overweight at diagnosis they may only have put you on gliclazide rather than Metformin since Metformin has the tendency to make you lose weight. As VBH says, it could indeed be LADA (Latent Autoimmune Disease of Adults) which is a sort of slow onset Type 1. It's not quite T1 but may as well be, once your pancreas has given up you will do well on insulin with no oral meds if you are indeed LADA. Should it be too late for any GAD antibodies to show up then a C-Peptide test could be done to see exactly how much of your own insulin you are producing. A low level would be indicative of LADA.
However, before jumping to conclusions I would ask do you know the carbohydrate content of that wholemeal bread? My husband has wholemeal bread which is quite high in carbs, whereas I eat Burgen Soya and Lindseed, only 11g carb per slice. Also as Adrienne states, if you were high prior to eating the sandwich it may just have pushed you higher. However, if that were the case, the question would be why exactly you were high before the sandwich. For example how long since your last meal and what was the previous meal. What are your FBGs these days, have they risen? If you could please give a lot more information it would be easier to get to the bottom of it.
I was diagnosed T2 (due to my age, but I was very underweight at diagnosis) and put on gliclazide only, however I progressed very quickly, within a few short weeks onto insulin and thence all oral meds were dropped and I've been perfectly well controlled on insulin only for the past 6 years.
