What Causes Fever And Chills After Appendix Removal?

My husband had his appendix removed Christmas day and has not felt good since then. Sunday he started running a very high fever, had chills and sweats. He went to the doctor yesterday and they said he has blood in his urine and his liver enzymes are elevated. They did an xray of his abdomen to look for any blockage and there was none. He has zero energy and sleeps most of the day. He is 53 years old, not overweight and does physical labor for work. He does take pain medication for his back, he installs wood floors for a living. He has not had an appetite and he cannot eat very much at all. He still has a mild fever that comes and goes. He did take several doses of Sambucol, originally thinking he had been exposed to the flu, however, he tested negative at the doctors office. I am concerned him may have sepsis. The doctors office just called in an antibiotic and want him to come in next week for additional testing. Is there anything I should watch for that would warrant a trip to the ER?