I would definitely address this with your doctor. But as CJ stated, anxiety can also do this to you, as well as depression. Also, always being pre-occupied with other things, constant worrying, etc. Talk to your doctor to rule out any other problems that may be causing this. Take care...
Have you talked to your doctor about this? Are you under a lot of stress or suffering from anxiety right now? In my experience, whenever my nerves are up my short term memory goes out the window.