How To Treat Dizziness, Stomach Pains And Loss Of Appetite Before Colonoscopy?

My 78 year old mother has been expeincing the following for the past few months, nausea, dizziness, stomach pains and loss of appetite. She had an upper GI done and they only found slight tenderness in the stomach. She was scheduled for a colonoscopy twice, but was unable to keep the drink down and therefore had to cancel. She is getting very weak. Her past medical history, she is diabetic, has had 3 stints put in, one minor stroke, and has high blood pressure. What could cause this and what should be the next step?