What Causes Short Term Memory Loss After Back Surgery?

I had back surgery in 2010 when I was 65 years old. Since that time I have experienced memory loss, mostly short term. I was evaluated by Ph.D.,ABPP, Board Certified in Neuropsychology, for fear of the onset of Altzheimer's. The Doctors evaluation concluded that a OTC sleep aid used due to my husbands snoring was probably the result of my short term memory.
I am seeing a endrocrinologist Monday, due to my PCP's concern over my Thyroid levels. Something is wrong with me and it all started after the 2010 surgery.
Dr. everyone claims the anesthesia was not the cause, it not that what?