Make sure you are mixing 2tbs lemon and 2tbs maple syrup. Some times if you don't get enough maple syrup in there it will sap your energy. I am on my 6th day and I have felt full of energy the entire time.
I also take powdered spirulina in a little bit of fresh juice in the morning and sometimes in the evening.
If your feeling too weak maybe you need to take it a little slower and get some nutrition in you. Just a little to give you a boost. Like fresh broth.
Some people will feel tired, achey and get headaches from day 1 to 5.
Make sure you are drinking at least 6 lemonades a day if you are feeling weak. How many are you drinking?
As for doing something unhealthy, This is very healthy,it's getting the toxins out of your body and also giving your organs a much needed rest.
Hang in there, keep asking questions.