Looking for a possible diagnoses based on these symptoms: mucus in the back of the throat, sore throat where mucus is in the back of throat, stiff neck , really painful headache, nausea, loss of appetite, joint pain, slight muscle pain, exhaustion, sweats and chills. Started out with full sore throat, sore neck and headache. Nasal passages have been clear. Mucus build up has only been in the back of throat.