Hi. Thanks for your query. Noted the history and understood your concerns. Sleeve gastrectomy is a a major surgery with implications all over the body as this is done to reduce the weight. Hence initially a large part of the fluid, electrolyte, protein, carbohydrate and lipid metabolism will be altered and it take time for the body to cope with the sequel of such a major surgery along with major internal changes. This may be the reasons for feeling fever and weak. But at the same time we have to rule out any other medical condition like infection that might have been present in the body by the following ways: Tests of blood: Full hematology including culture and sensitivity of the blood, electrolytes, sugar , hormone status including that f parathyroid and insulin. X-ray, preferably CT scan of the chest and abdomen to see for any infection focus. Proper antibiotic coverage. Regular follow-up and management should help you to come out of this unusual problems after gastric sleeve surgery.