I have been Fasting for over 20 years. My first fast when I was a teenager for 11 days !!! Have done 14 to 16 days safely-and I am not overweight...and More 22 is my record...and with Water only. You have the added Luxury and nutrients of the Lemonade which should help as well.
A Good Indicator if your Body is Ready to end a Fast--look to see the conditon of your tongue. The white coating disappears after say 14 to 16 days. You have to Worry When your tongue begins to bleed--the Tip of your tongue. THEN is when your fat reserves are used up!!!

OH--if you are Really Worried about losing too much weight--add some Protein powder to your lemonade instead of the maple syrup...

You sound pretty thin to begin with and you will probably lose some weight while fasting. I'm not sure about if or how much muscle mass you might lose. You might want to go on a cleansing diet instead that incorporates lots of organic vegetables and fruits, salads, and fresh vegetable juices. Although the cleansing process will be slower, you will continue to get vital nutrients. Since you're new to fasting you might want to try a 1-3 day fast and see how you do. There are many ways to detox including colon cleanse, liver cleanse, liver/gallbladder flush, parasite cleanse,saunas, dry skin brushing, in addition to fasting. I'm not trying to discourage you from fasting...just letting you know there are other ways to clean yourself up if detoxification is your primary goal.