Hi, I am sorry for the health problems you are going through. Shingles is a contagious viral infection that will take a few weeks until totally recovered. Antivirals started will help reduce the period of rash and pain (which are 2 most common signs of shingles). As for any other drugs, antiviral use is often associated with side effects including headache and nausea. They are temporary and will go away after you stop this medication. With regards to not being able to eat much, that is partially from shingles infection itself and antiviral use too. That is temporary too. I advise to keep taking the rest of antiviral (I believe not much is left) in order to succeed in treating shingles attack although your symptoms are diminishing. Try to keep well hydrated and have frequent and small portions of meal until fully recovered. Wish fast recovery.