Okay, have you tried other carb foods such as pasta, potatoes and rice? What affects do those have compared to the bread? Also, what kind of bread is it you eat? That's really strange. If your blood sugar is normally high, and then go down to a 'normal' level you may experience those shaky feelings. But it doesn't sound like yours is high.
I know nothing of what's in a taco salad as we don't have them here but I'm presuming no carb. When you get the shaky feelings, try something else carb based to see what that does - have you seen whether a cereal such as muesli does the same thing?
I know how frustrating this is, believe me, so just hang in there and I'm sure between us all here you'll find a solution! Having diabetes requires patience, I think, so stick at it!
Best of luck x