Stupid question, but need answers...

I have been having some issues like getting real tired after eating breakfast. It doesn't happen every day, but more often then not. I also have a number of other symptoms like excessive thirst and so on.

I was just wondering how Diabetes is diagnosed. I have had my blood sugar levels tested by the little stick in the finger, and that is always normal.

I do have a pretty high c-peptide. (1230 where 1400 is the high end limit). I'm not sure how much that has to do with diabetes even tho I was told by a friend that it does mean something.

Any replies would be greatly appreciated.

Thanks!