Hi, My 68 Year Old Husband Who Is Healthy Has

Hi, my 68 year old husband who is healthy has run a temperature of 100-101 degrees since last Wednesday. CBC was normal. He is fever free in the morning and feels ok, although he is weak , I'm assuming from the fever. However he runs 100 degrees temp in the late afternoon. For the first day or so he had slight nausea and diarrhea but ever symptom since then. He went to his PCP yesterday. Lungs were clear, as were ears and throat. Do you think it could be some sort of tick related illness? Help!