Oh, having a bunch of parasite eggs explains a lot. Did they say what type of parasites?
So, you ended up taking him in, great that he was so good. Hopefully once the eggs are gone, he will start eating a lot more. What was his coccidia count or didn't they tell you?
Make sure to put him on a probiotic right away and to continue it for about 3 wks after the medications are done to help restore his good gut flora so that he doesn't lose more of his appetite. Also, antibiotics are very drying so be sure to offer oral fluids and give daily baths.