My son is experiencing sore throat, fatigue, appetite changes (quality: reduced appetite) and loss of voice.

Dr. can check throat: New throat pain can be from a strep throat infection (antibiotics are needed), a cold or influenza (antibiotics usually not used), or from some other cause such as allergies or irritants. Usually, a person sees the doctor if the sore throat is bothersome, recurrent, or doesn't go away quickly (mainly to check for strep throat). A couple days of throat lozenges and Tylenol (acetaminophen) can help.

Throat: Time to see Urgent Care or primary Dr. Sounds like pharyngitis/tonsillitis, but needs checked for more serious complications. Strep test may be reasonable. Meanwhile, Chloraseptic / Cepacol / similar may help with the pain enough to allow hydration. Good luck.