This sounds very much like a severe Candida infection. There is only one thing that coats the tongue and that is fungus.
Lufenuron works the best but you can try Oregano oil and/or Colloidal Silver .
Candida/Fungus prevents proper vitamin and mineral uptake in the body resulting in ALL the symptoms you describe. Be aware, the fungus invades after the parasites have moved in. Sorry. Kill the fungus first or at least reduce it. Lots of info on CZ. Read Read Read
Many people can't accept they have parasites because they have never seen them. Everyone has parasites. It's just a fact.