It's very common, and even has its own names such as Cancer Related Fatigue, Chemo Induced Fatigue, etc. and forget what acronyms they use too, to help in your search options. NCCN, National Comprehensuve Cancer Network, has its own guidelines for clinicians too, but I can only copy the 2014 version. Many centers and organizations have addressed this, but I think it's still often unrecognized in individuals.
I have chronic fatigue the past 7 years, which somewhat improved, but it could be better, and at times, not ny main concern.
I have read dozens of articles, which I try to apply in ny situation, which is basically to have a full physical, stress test with complete blood work some to include vitamin D, B12, TSH, PTH, A1C1, Creatinine, Hemoglobin, etc. and to correct any deficiencies your doctor prescribes.
Do they check you BP from seated to standing? Mine never did, and diagnosed myself with orthrostatic hypotension, which they verified. I also requested to have a carotid Doppler exam (ultrasound) to check any artery blockage.
Conserve energy where you can. I use a shower chair, and sit, instead of standing, while cooking and doing prep work.
Exercise is often prescribed. Maybe with Physical Therapy first, light walking. Yoga, Thai Chi, meditation may be beneficial and many cancer centers offer free classes
Improve sleep or it can be too much too? Some have sleep apnea, I did for a while.
Check medications as so e may have tiredness and other factors causing fatigue.
Maybe see a registered dietician or nutritionist. Get adequate nutrition and hydration. Limit caffeine, alcohol, sugar drinks, which energize you, but may drop your energy levels lower later on than they were before.
Counseling, therapy is often prescribed. Check for depression
Here are some good link that pretty much mentions everthing better than I can:
http://chemocare.com/chemotherapy/side-effects/fatigue-and-cancer.aspxhttps://s3.amazonaws.com/pfizerpro.com/fixtures/oncology/docs/NCCNFatigueGuidelines.pdfhttps://www.nccn.org/patients/resources/life_with_cancer/managing_symptoms/fatigue.aspx 
