Well, Lick it if you have to. But don't stop. What are you fasting on? Water only?
Maybe some juice or chicken broth, if you want to keep fasting. Or if you need to chew, chew celery.
Your tired because your body is getting rid of all that icky stuff that you've been storing up when you were eating all those grilled cheese sandwiches. Did you ever take a real good look at a slice of American Cheese, or the ingredients?
I think it's hard, but you'll be psyched if you keep going. What I started doing is saying my weight all day. Everytime I stop thinking about something I say my weight for that day. So, do I want to be # tomorrow, or do I want to be #. I know right before I look at that bag of chips and I say my weight and my target weight, and realized I don't want those chips.