I Have Had Non Hodgkins T-cell Lymphoma Twice With High

I have had non hodgkins t-cell lymphoma twice with high dose chemo and a bone marrow transplant using my own cells. It has been 7 yrs. since the last one and recently I have been feeling weak and unfocused. I had a brain MRI and my dr. prescribed aricept, but said I do not have alzheimers. What do you think?