High fever. Otherwise normal , esr: 20!

Hello there. Im asking this for ny brother who is suffering from high fever from the past 8 days. At first day his fever was 104 at max we gave him crocin fever came down to 100. Till 5th day his fever was around 102..but from the last 2 3 days his fever goes upto 104.. last night also his fever was 104 we have noticed the fever rises during the day and at night mostly at night.. other than this he was complaining headache,chills.Widal and typhidot test was done on the 6th day which says: widal- typhi o at 1/80, igg and igm were negative, test was repated again today (after 2 days from the last tests)  which says: widal- typhi o & h at 1/80, igM positive and igG negative.He is currently taking crocin and augmentin 625. I want to know whats causing the fever. Following tests were also done which came out as following: Kft normal Lft : sgpt- 46.8, sgot- 53.20 (slightly high from the normal),Chest xray normal, Urine culture normal ,Cbc: normal but hb is 11.2 otherwise normal ,Esr: 20