What Causes Short Term Memory Loss Along With Mental Confusion?

I have been experiencing more frequent forgetfulness and making mistakes at work the past couple months. I can't multitask as well as I used to. I have trouble focusing. It is becoming a problem at work. Also a lot of muscular pain, especially in my neck, shoulders and back. More severe pain in the mornings and evenings. By 2 in the afternoon, it is like my brain shuts down. I get at least 8 hours of sleep every night, but still have a hard time getting up in the mornings, sometimes from the pain. I don't do much socially any more because I feel bad so much of the time. I am a 58 year old woman. I take estradiol daily, also some asprin and ibupropen frequently for the pain.