Hello and hope you are doing well.
It could most probably be tonsillitis and a throat infection. Throat pain, difficulty swallowing, fever, scratchiness in the throat, post nasal drip, malaise and loss of appetite are symptoms of tonsillitis. It can be caused by bacteria like streptococcus or it could be a viral infection. Bacterial infections need antibiotics. Consult your primary care physician who will do blood tests and take a throat swab to determine the cause and prescribe appropriate medications. In the meantime, you could take OTC multivitamins. Take plenty of warm oral fluids and lots of rest. For further relief from your symptoms you could do warm salt water gargles and steam inhalations. Please ensure to do this prior to your meals.
Hope this helped and do keep us posted.