My recommendation is to first accept that your motivation is going to wax and wane on this long weight loss journey. I know that sometimes I'm a happy little cheerleader for health, fitness and weight loss, other times I just want to bury myself on the couch with a packet of chips and not come up till October. This is perfectly normal so you're not being bad or lazy by losing motivation temporarily. Just remember that it's only temporary and think back to times when you were 100% committed to your weight loss. If you remember how you felt, it seemed that nothing would stop you at the time. You'll get back there again, trust me. If necessary try some creative visualisation. Close your eyes and remember how motivated you felt back then. Now picture yourself at your goal weight feeling that motivated. This will help link the two concepts in your subconscious so that you will get some drive back.
There are two things to consider: do you just need a rest for a bit? Or are you just wanting to go back to your old, bad habits? If it's the former then maybe you need to cut back for a week. Keep eating healthy food, but maybe lock your scales away until your head is back in the right space. If it's just that you want to start eating your own body weight in Tim Tams again it might call for more drastic measures. As Tegan said, remind yourself in writing why you want to lose the weight so much. You've already come a long way, but there must be reasons for you to want to continue to get to your goal weight - even if it's as seemingly superficial as wanting to fit into a bikini by summer, or wanting to buy size 10 jeans.
One sure fire way to get your motivation back is to 'fake it till you make it'. I know that the times I hate exercise most is when I haven't done it for a long time. My body just can't remember how good it felt to exercise, so instead I focus on how much I hate it. Don't let these bad attitudes back in. Force yourself to go and exercise. Within minutes you'll remember how much you enjoyed it. Make yourself eat a salad with your dinner. Focus on how yummy it is and soon your mind will agree with you. Keep this up for a week or so and a positive attitude towards health and fitness will just start to come naturally.
Constantly give yourself positive feedback when you're doing something healthy. Rather than go for a run thinking 'I hate this' think things like 'I feel great when exercising', 'I am strong, fit and HOT', and 'this is FANTASTIC!' The mind is a powerful thing. If you repeat something at it often enough it becomes gospel. Especially if you put feeling behind it. If you tell yourself you hate something and feel miserable while doing it you are deliberately setting yourself up to hate that task. If tell yourself you love something and really enjoy it you are going to start to like doing it even if you are lying to yourself at the time.
1. Accept that you're not going to feel 100% motivated 100% of the time.
2. Pat yourself on the back for the huge amount of weight you've lost so far. You've managed to lose weight before so you know you can do it again.
3. Write down a list of reasons why you still need to lose a few more kilos. Focus on the positives 'I'll look hot in a bikini' rather than 'to get rid of my stomach rolls'.
4. Close your eyes and visualise. Link the feeling of motivation and feeling great, sexy, fit and thin with a mental image of yourself at goal weight. Do this at least once per day.
5. Give yourself a couple of days rest if you need it.
6. Fake it till you make it. If you don't feel like going for a walk, go for one anyway. Tell yourself how much fun you're having while you do it!