If you're really just struggling with work, it may not necessarily be a problem with alertness, but motivation. I'd recommend trying to externalize your motivation. So, if you want to write a novel, you'd join a writing class. If you wanted to be more organized, you might put alarms on your phone to remind you to stick to your schedule. If you can find a way to do something like this at work, you might have a much easier time getting things done.