Long term use of letrozole

I was diagnosed with breast cancer 6 years ago and after a mastectomy and reconstruction was put on letrozole. I understood at that time it was for 5 years but have now been told I need to take it for 10 years. 


I suffer badly with fatigue, dizziness and difficulty getting to sleep. I also have fibromyalgia which I have always blamed for the muscle pain I get and other associated symptoms. I’ve also having bad problems with my eyes which has been put down to cateracts, but I’m not so sure. 


Has as anyone any suggestions about long term use of letrozole and its symptoms.