Hang in there. The yellow and blue menus are designed to get you into ketosis and help you to lose weight fast. You lost so much in pre-conditioning so I wonder if you may just not be getting enough calories.
Do you work our a lot? Anyway, the one issue I've always had with MRC is that is a "one size fits all" menu. I'm only 5'1" and my menu is the same (quantity wise) as someone who is 5'8". That doesn't make sense.
Anyway, too many diet drinks have shown to slow weight loss. Also, I think it's a way to get rid of cravings of all kinds.
Anyway, the best thing is to drink lots of water during this phase. If you are really hungry, you might also want to add an extra HNS. And if all else fails, drink the diet soda! It's better than going off plan with food.
Hang in there. It does get easier.