Blood tests showed sodium 141, potassium 4, chloride 99, bicarb 22 which gives me a high anion gap of 24. As I am fatigued could this indicate cancer?

No. and your anion gap is only 20, according to the numbers given, (usually potassium isn't included in the equation). Anion gap calculation isn't used to screen for cancer, rather metabolic problems, commonly acidosis, and several disease contribute, as kidney, gastrointestinal (diarrhea), drugs, diabetes, etc. Lab errors need to be excluded, and most important is clinical correlation, u r fine.