What Causes Extreme Fatigue Along With Appetite Loss And Stomachache?

My mother-in-law has been suffering with extreme fatique, loss of appetite to where she s losing weight every week, stomach and head pains, and at times a feeling of all blood drained from her, feeling just strange. Her father died of stomach cancer, one sister of colon cancer, another sister had breast cancer and died of pancreatic cancer. My mother-in-law also had colon cancer that was caught in time.