It is getting cold and most likely your race season has come to an end. Take it easy for a few weeks after your last race and make sure you get back in the swing of things quickly. Don't take too much down time. Use the off-season to build some of your weaknesses and make your strengths even stronger. If you need a lot of help in the pool then you should be getting in the pool a minimum 3 days a week. If you can you should be in the pool more than three days a week. You don't have to swim long each time but a weak swimmer will only get better by swimming more often. If you have a run one day then hop in the pool for a quick swim after your run EVEN if its only a 20 minute swim. In the cold weather getting in the pool is tough but you have to do it to become a better swimmer. If you are a weak cyclist then getting on the bike 4 to 5 days a week is a good idea. If possible 2 of those days should be outside and 2 on the trainer. Your trainer workouts should be targeted interval workouts, don't just get on your bike and ride. I recently found a good website that will help break up the boredom one the trainer. The website is www.trainerroad.com. There are tons of workouts to choose from for only 10 bucks a month. Running is no different than biking or swimming. If it is your weak area then maybe find a 5k, 10k, half marathon or marathon to train for in the winter. You can almost always find local running events all year around. The shorter distance are good to do leading up to the longer distance. They will also help keep you focused.
If you still are finding it hard to get motivated this time of year then find some groups. If you are a weak swimmer then join a local masters swim group. If you are a weak cyclist then find a group to ride with. The same applies for running. Getting a coach will also help keep you focused in the off season and will help you maximize this time of year. This is a VERY important time and will be key to your success in the following year.