Honestly the concept of motivation is overrated. Sure you need something to drive you to get to your goal but you have to make the decision daily to eat right and exercise. There are going to be days you're not going to want to do it, but do it any way.
When I first started out, I approached it as living a healthy lifestyle for the rest of my life. First you have to identify what areas you're having problems in that have lead you to where you are today. If it's your eating habits for example, if you're a sucker for candy bars, replace them with healthier alternatives like fruit. I used to eat 2 king size snickers bars a day...I have replaced them with 2 servings (1/2 cup) of trail mix. The trail mix has several different types of nuts, fruit, and a few m&ms for a lot less calories. Same great taste, a lot less calories.
Snickers (1 king size bar)
528 calories, 22g fat, 73g carbs, 10g protein.
Trail mix (1/4 cup):
160 calories, 10g fat, 12g carbs, 5 protein
Comparing those 2, I get the same great taste but for much less calories. Here's the 2 serving count for each:
Snickers: 1056 cal, 44g fat, 146g carbs, 20g protein.
Trail Mix: 320 cal, 20g fat, 24g carbs, 10g protein.
That's a difference of 736 cal, 24g fat, 122g carbs, 10 protein. Just by choosing a healthier option.
That's just one example of something I changed in my life. If you find something similar in your eating habits, if you only change 1 thing and keep everything else the same, look how big of a deficit you're creating by a simple change like this. Make a few more changes like this and over time, you're not only going to lose weight, you've just found something that you like so you're going to be able to stick to it going forward.
If you're lacking motivation to work out, try this for a month. Put your workout clothes on. If you have a gym membership, drive to the gym, get out of your car and walk in. If you're still not motivated to workout, turn around, get back in your car and go home. I'd be willing to bet that 95% of the time that once you're there, you're going to put in the work. I've had the same thoughts but once I get to the gym, I'm ready to get after it. Or once I throw in that workout dvd, I'm ready to do the work. Don't let your thoughts hinder you from your goal. There are going to be times when you'll be working out and just don't have it and that's ok, stop...at least you gave it a go and did something rather than letting your thoughts stop you before you even tried.
I've had times were after 10 or 15 minutes of lifting or cardio, I just didn't have the focus I needed to get it done so I went home, that's normal, but those days are few and far between.
Anyway, those are just a few examples. Sure motivation is nice, but you've got to treat living a healthy lifestyle just like you would anything else. How many times do you wake up in the morning and aren't motivated to go to work? Do you call in to work and tell them you're not motivated to be there so you're staying home? Heh I think not...do you "have" to work? No, but the benefits of working are you make money to provide for yourself and/or family. So you drag yourself out of bed and go to work. Living a healthy lifestyle is no different. Do you have to live a healthy lifestyle? No, it's a choice but the benefits far out weigh not living a healthy lifestyle.
You can see what helped me lose 146 pounds over the last 2 years here: www.sparkpeople.com/mypage_public_journal_
Hope this helps! Good luck on your journey.