Hmmm. A total fast may be a catch 22. Say it ends up being parasites/worms, then you want your bowels to be moving to push them out. Maybe if you are still taking that stuff, but still. Actually I should mention that a dose of castor oil after a day of garlic and onion might push something out. That's an age old remedy that I can say does work.
Not knowing what your real situation is yet, I would not want to recommend anything to you that could make you sicker. Me personally, I have fasted for a day or two and had great results.
There are lots of foods that you can eat that are pretty well accepted as anti-parasite. Pineapple, pumpkin seeds, Greens, peppers, papaya (and the seeds crushed), there is a pretty long list.