You may think you suddenly have adult ADD but chances are, you just need sleep! Lately, you're distracted by anything and everything. Even the sound of the wind will make you lose your train of thought. If you have a baby that still wakes up at night, chances are it's actually sleep deprivation. If you feel like lack of sleep is affecting your productivity at work, due to lack of focus, maybe consider temporarily cutting back on your hours until you can get a handle on your baby's schedule.
If this isn't an option, try adjusting your work environment to eliminate as many distractions as possible. If you work in a cubicle, see if you can be moved to a quieter area. If you're right in the middle of the room, you'll have to put up with more noise and "traffic" of people walking past your desk. Of course if you're in an office all you have to do is shut the door and close the blinds, if there are any. Also, remove all the little things off your desk that will take your attention away from work. This includes pictures, paper weights, etc. For some people, wearing headphones and listening to music also helps them to zero in on the task at hand, while others need complete silence. Figure out what works for you, and then do it.