In addition to other things, I find both headaches (generally migraines for me) and the weather can affect my glucose levels. Since I can't control either, I try when in this situation, not to make my levels any worse by stressing over them.
Sometimes you just have to accept that such things happens, and are often beyond your control, though it certainly helps if you are aware that things other than diet can cause them, and that you're not (necessarily) doing anything "wrong"!
Robbity
PS Are you keeping any sort of food diary so you can see what may be causing any spikes? 29g carbs instead of 28g is neither here nor there, and particularly in the case of veggies and fruit, nature will never be absolutely accurate. The values we're given for their carb content can only ever be an average taken over a number of test batches.