Fever , more body pain. Feels body pain!

My dad is stage 4 stomach cancer diagnosed 1 year 11 months back. After chemo complete metabolic response after 5 months. He was on capacitabine maintenance chemo for a long time. Then we got to know cancer back in a few spots in the liver and stomach. My dad refused any treatment and 9 months he was fine working, walking. 6 days back he got high fever, full body pain, one leg pain severe, from 5 days he has fever 103 at afternoon and night. After 5 days it was 100.5 but still his body pain not gone. Cbc we performed normal, dengue ,malaria etc, xray and ultrasound scan normal. Everything is normal. He is admitted that a hospital pain killer has been given. He has little chest mucus, when he tries to move to spit he feels body pain