From what I have been reading it can be a very difficult thing to "catch" because not everyone's reaction to the glucose is the same and in order for Dr to Dx it has to fall within specific parameters and if you are outside those parameters, then no Dx even if you have every other symptom there can possibly be. This can also be the same with hypoglycemia, which is even more difficult to get a Dr to Dx and some don't even believe it exists, strange but true!
Also, I have heard mention that you need to have your insulin level messured and not blood glucose during those 2-6hr glucose tolerance tests. I got my own glucose monitor (you can get them for free online, but have to pay for test strips which are $$$$) and spent several days monitoring on my own. I would right down what I ate and then record every 30 minutes... this was $$$$, but since I couldn't get a Dr to pay attention to what my gut was telling me, and I wanted to know, I spent the money. I recently read that you can go get the same glucose drink at the pharmacy that the lab gives to you before the test.
Regardless of being Dx as being IR, you will do no harm (and probably benefit) from treating your diet as if you are. and Metformin is Rx for both IR and non-IR PCOS, so a Dx of IR shouldn't matter in getting a Rx for medication... if your Dr won't Rx Met w/out IR Dx, then perhaps you should bring in some research articles about Met & non-IR/Obese PCOS treatment or find a different Doc who is up to date on medication treatment of PCOS. | 
