Have you checked to calibrate or change your meter? If the calibration is wrong, then you're numbers could be off, though this doesn't happen often it is possible. Especially if you don't feel particularly bad when your sugars go up so you wouldn't know. I get sinus pressure when my level raise above 190 so it's a good giveaway, but that just started happening the last year and everyone is different.
If your Hba1c level is rising, but your pre and post BG levels are good, then you probably need to look at the times of the day when you are not currently testing, e.g. at night. One way to do this is just to set an alarm clock on different nights at different times, or you could try to get hold of a continuous blood glucose monitoring device (CGM) which are now beginning to attract insurance approval.
Your Hba1c rise must be caused by high BG somewhere: you just have to find where and when, and then work out a fix with your doctor (if it's a sudden rise in the early hours, you might want to look at an insulin pump if you're not already using one).
Good luck!