early symptoms?

Over last year adult male in good health age 66- problems with short term memory, working with detailed items, more dyslexic in writing, aversion of people i.e. more reclusive, wanting quiet not interaction (mental "overload" trying to cope with the action}, frustration with detail items and processing detail information to troubleshoot or analyze, edgy and prone to short temper,  
No headaches or any physical symptoms, sleep ok, etc.
Short and long psych tests show memory deficiency, unable to complete the long one due to overload, MRI of brain shows normal, etc etc.  Review by Univ of Mich Gerentology specialists gives no diagnosis.
All appeared about 15 months ago at age 65 and has compromised quality of life, the adjustment is quite difficult, day to day life becomes a struggle overcoming the above.
Realized after reading about drug interactions and induced dementia (yes its me, but I can still think and touch type!!!) that I changed from Claritin to Allegra for control of perennial allergy symptoms.  And was initially started on 60, then a check of my records shows that after 3 mos I was upped to 180 and did not realize it.  Have been on 180mg for 14 mos, and just dropped back to half pill or 90 mg.  
My overall composure is definately better, less uptight, etc, tho it appears many of the first mentioned symptions are still here they seem easier to cope with?????????
Comments (both on evidently lack of diagnosis and on the antihistimine doses) really appreciated since I/we are really groping for ideas/assistance.  
Initially the words Alzheimers was used but it was dropped....
Currently using psychologist to assist with coping, time for retesting etc but that seems like an exercise in (further) frustration.

L.

[CCF-Neuro-M.D.-RPS]

Dear Larry:

Sorry that your having troubling symptoms.  Memory loss is a common occurrance as we age.  Whether the antihistamine is inducing changes, I can't tell from here.  Theoretically, the formuation in Allegra or Claritan should not pass the blood brain barrier and hence should not caused CNS side effects. However, we have all seen CNS side effects in a few select.  Since you have lowered the dose and are feeling better, this might be the answer.  Why don't you completely go off the antihistamines and try something else?

Sincerely,

CCF Neuro MD