Suggest Treatment For Nausea , Hyperosmia And Diarrhea

My 80 yr old Father has developed hyper sensitivity to smells, taste (everything tastes awful), has constant nausea, diahorrea, lethargy and has been sleeping a lot over the past 3-4 weeks. He isn t eating or drinking very much. Do you have any advice? He is reluctant to go to a GP because he feels the symptoms are vague.