Why is my blood sugar levels dropping so quickly?

My mother has type 2 diabetes, but I do not. We recently both went a low GI diet (making sure to eat enough calories though), and my mother's blood sugar levels stabilised better than they have in a long while. Mine, however, kept dropping rather quickly to just below 4mmol/67md/dL. I started to shake and became very tired, even after I tried eating some fruit to bring the level back up. My diet until recently has been terrible (mostly high GI carbs, little meat, and little veg). Is my body just rebelling the new low GI diet or should I go see a doctor? I've been doing it for four days now.