I am no candida expert at anything, but I will put in my two cents on what the problem could be.
I think the very small amount of sugar in the lemon is what is causing you problems Thomas, so maybe try it again in a few weeks. I believe there is 2.5 grams of sugar per lemon, which is about the same amount as a whole onion.
If this isn’t a problem, it may have to do with the alkalinity/acidity of your body and could be putting it out of balance.
Or, the lemon and the itching are not related but just a coincidence.