What Causes Weight Loss Along With Extreme Fatigue And Hot Flashes?

My symptoms are as follows, nausea, weight loss of 40 lbs. in six months, extreme fatigue, hot flashes, sweating, pain in upper, center of stomach area. I have had a gastric bypass, her at that incision repaired, colon resection from diverticulitis, complete hysterectomy, 2 spinal fusions and a spinal cord stimulator implant 7 months ago. Thanks for your help!