Hi thanks for posting your query.I have gone through your concern..fever in theeldery can suggest a wide variety of causes.the basic cause for which one need to evaluate are-malaria,typhoid,hepatitis,meningitis,gasteroenteritis,all genital tract infections,chest infections,bacterial infections ,viral fevers etc.since his fever is continous pattern,you need to evaluate through certain set of investigations which include--complete blood counts,hemoglobin %,esr-erythrocyte sedimentation rate,blood urea,serum creatinine,complete urine examination,chest xray,qbc for malaria,widal test for typhoid,serum hbsag,vdrl....in case of headache,lumbar puncture with csf exam is useful.based on the results of these tests,you can conclusively arrive at a precise diagnosis.treatment for fever includes cold/tepid sponging,antipyretics like paracetmol 650mg three times a day.emperical antibiotics like tab augmentin 650mg twice a day,until results of tests are out.complete bed rest is adviced till revovery.specific treatment depends on the test results.consult your general physician in case of need.thank you.take care