Just F...... do it!! Think about it and whine about it AFTER you have done it.
We spend too much time talking ourselves out of exercise and don't even realise it - catch yourself out!
The other thing is, challenge yourself with food. Say to yourself - "I am going to eat more vege's and less cheese for 2 weeks" and see how it makes me feel, then re evaluate again after this period. It is a great way to improve and test certain things...and move forward without doing too much too soon.
Also, every night just before closing your eyes, spend 5 mins visualising and doing your exercise, enjoying it and feeling great. Try this...and see for yourself!