Suggest Treatment For Persistent Tiredness And Loss Of Energy

I m 76 years old, andI have several problems. The first is Dementia according to my Neurologist, and I m now taking donepezil 10mg for that. The next item is gastroenterology. My GI has me on donepezil 20mg, and it seems to create a lot of gas which is all day and all night, which I haven t had a chance to tell the Dr. about it. Lately, I seem to have become very tired, no energy, and difficulty sleeping which is very unusual for me. I normally feel like I m in my 50 s with lots of energy, and never get tired. Within the last three days, I m week and there are times I feel like I m going to pass out. What should I do? Would ProBiotics help, and if so, what kind should I buy.