I have been a 'borderline diabetic' for years, and it sounds like your blood sugar level is crashing. I usually get extremely hungry, dizzy, clammy, nauseaus, lack of concentration, and confused.
Definately keep eating every 2 hours. Your drop is most likely happening between the 2 - 3 hour mark. That is when I always experience mine. Try eating snacks/meals that have more complex carbs to them. That way your levels don't drop quite as quickly or drastically. For example, eat scrambled eggs with wheat bread vs. pancakes. Things like that. Also, you should buy some orange juice. Orange juice is the fastest, safest, and quickest thing to raise your blood sugar. I'm not pregnant so I grab a Coke, but you are. Orange juice would be best for you. Also keep lots of crackers on hand.
You may or may not know this but liquids bring sugar levels up within 5 - 10 minutes. If you consume food with a low sugar level, you will continue to drop because food takes about 30 minutes to raise your level. ALWAYS CONSUME A LIQUID OVER FOOD WHEN HAVING AN INSTANT DROP.
***A SIDE NOTE***
Since I have been 'borderline diabetic' for years, I see an endocrinologist. As you probably know, I have been TTC for 2 years. Well, my high-risk OB/GYN was VERY CONCERNED about these plumits while pregnant. THEY CAN EFFECT THE BABY IF LEFT UNATTENDED FOR TOO LONG. I would call your doctor and inform him/her about your episodes. They will most likely tell you very similar things to what I just have, but at least they are aware.
My doctor never really said what can happen, but that it must be avoided. Like I said, I haven't been there.
If I were you I would try and eat something every 2 hours to prevent the drop. Don't wait until it happens, moreso with being pregnant.
EDITED TO ADD: I OFTEN FEEL LIKE EVERYTHING IS IN SLOW MOTION!!!