Mike's analogy of the car is perfect. It does get WAY easier once you build momentum, but you still have to work a bit to keep up progress.
You need to find in yourself the motivation to accomplish this goal. This is a real challenge (perhaps your first real, grown-up challenge) but if you're up to the task you'll succeed in due time, just remember that the onus is on you and no one else. The effort you put in--and how you apply that effort--will determine your success. Fortunately, you are in something of a full immersion experience (aside from your home life, presumably), so you have endless study resources surrounding you. TV, radio, books and magazines, signs, menus, and most importantly, people. You have a wealth of opportunities to use your Japanese, and each time you flex that muscle, it'll get stronger. Good luck.