If you are having trouble sticking with a fitness program, the Mayo Clinic offers these tips to help you stay motivated:
Set goals: Start with simple goals and then progress to longer-range goals. Keep goals realistic and achievable.
Start slowly: If you push yourself too hard at first, you may be forced to abandon your program because of an injury. It's best to start slowly and progress gradually
Think variety: Vary your activities to keep boredom at bay. Alternate walking or biking with swimming or low-impact aerobics classes. Have fun: You are more likely to stick with a program if you are enjoying yourself. If you aren't having fun, try something else.
Make physical activity part of your daily routine: Don't fall back on excuses. Schedule workouts just as you would any other important activity.
SOURCE: MAYOCLINIC.COM