This is about my father. He is having fever (low grade 99 to 100) with body ache everyday in the evening. He had the same problem 10-12 years back. He was hospitalized for a month, but nothing was diagnosed. About 2 years back he was diagnosed with stone and TB in urater. He was operated for the stone and took medicines for TB. He was well then, no fever or anything. A few months back he was also operated for hernia in abdomem. Now from about a month the fever n bodyache is back.
Thanks for asking in Chat Doctor forum I understand your concern for your father. Evening rise of temperature before might have been due to tuberculosis, so was subsided with treatment.  Urinary problems are very common in elderly individuals leading to fever and backache. So, please provide details regarding your fathers age, any prostate problem and associated illnesses like hypertension/diabetes for further suggestions.  All the best.