You've lost 30 pounds in 4 weeks? FANTASTIC! Right now you're just going through something very normal which happens on all diets. I'm on Medifast and my loses are much less then yours, but then I have less to lose.
I can't believe you'd even consider giving up on this diet when you're doing so well. I think the only other diet which has you eating less calories then MF is Optifast. Make sure you are eating all of your lean and green meals. Weigh your lean. If you don't eat enough, your body will go into starvation mode. It's important to have a doctor check you out also.