Diminishing Mental Alertness/memory

I can't put my finger on when this started, but it's getting worse. I can't multi-task at all anymore. I get distracted very, very easily. I can't complete tasks in normal amounts of time; it takes days. I can't focus to get things accomplished. My memory is so poor. I can't remember details of things right after i'm told. It's like I can't pay attention. I ask a question and am too distracted to listen and actually 'hear' the answer. I'm in my early 50's and used to get right on my tasks at work and get them completed. People could really count on me and I was one to come to for getting solutions to their work problems. I could really focus and if I didn't know the answers, I knew where to get them and did it quickly. Now the descriptive words I need don't come to me when i'm trying to write or tell something. I forget what I was going to do when I got home, tasks go undone that i'd wanted to work on. Is this a brain tumor? Alzheimers? Menopause? Anxiety? Depression? Normally i'm an upbeat, positive-minded person, not a depressed person. My dad had the start of alzheimers, but that's about it. Any help for me?