There are a number of things you can do to help you get and stay motivated:
1. Determine your "why". Basically, why are you working out? What is it that made you decide to do it in the first place? How important is that to you? You want to find something that you can always go back to, when the workouts get tough and you find your motivation flagging, you can think about your underlying reason for all this and get back on track.
2. Set goals. Fitness is a journey, and something that we should always be working on, but every journey has its milestones. A simple goal might be "complete a 90 day workout program". It could be that there's a 10k or tough mudder you want to train for. Maybe you want to get in shape for a wedding, or for a vacation. You might set goals for weight lifted with a particular move, or finally being able to hold Crane for 60 seconds. Whatever goals you choose, write them down & keep track of your progress. And find more goals!
3. Accountability. This is something that helped me a lot. Find people who are also going through a workout program, and interact with them, online, at work, or at the gym. Post about each workout, how it went, what you thought about it, any progress you made or hurdles you have yet to overcome. Encourage and cheer each other on. You can do that in this thread, over at the teambeachbody.com forums, on Fitocracy, or on social media. I did several Beachbody workout programs with groups on the teambeachbody.com forums, and it really helped keep me on track. You never want to be the person who disappears from the group
4. Consistency. Don't skip workouts. Especially if you're having problems staying motivated. Put the excuses aside & push play. One thing that helps me is having no distractions. I get up early, before my wife & son, to work out. I'm usually finished & showered before they even wake up. My workout room also has a door, so I don't get interrupted by our cats or dog. If I decide I want to sleep in, it becomes increasingly difficult to tear myself away from TV, chores, hanging out with the family, etc. to take an hour or so to exercise. So find a chunk of the day that you can consistently devote to yourself & make use of it.
5. Measure your progress. But not too often. Your weight for example can fluctuate daily. Instead, I recommend taking all your measurements when you start a program, and at 30 day intervals after that. Most Beachbody workouts come with a cloth tape measure and instructions where to measure yourself. Do it! Measurements are a far better gauge of your fitness progress than weight. Body fat percentage is also an excellent gauge of progress. Don't worry about accuracy -- instead, make sure you ALWAYS use exactly the same method, whether that's a scale, calipers or some other means. You may not have your exact BF%, but at least you'll be able to track changes in it.
Above all, don't give up!