Chaser -- Just in case scally's compassionate advice isn't doing it for you ;) you might stop and think about what motivates you to do anything. It always seems to me that we want to make changes, we have to start new behaviors with discipline, and over time assuming we don't falter, they either become passions (sports we love, for example) or just habits (you probably don't have to really convince yourself to go to work every single day, it's just a habit by now.)
In that period of discipline, in my experience, it's all about harnessing the things that motivate us. Usually it's not just one thing; usually to make big changes it takes several things working to motivate us all at once. For example, my former Governator, in his encyclopedia of bodybuilding, suggests hanging photos of guys you want to look like around your house as a reminder. For eating right, track your calories by writing all your foods down in a journal and use a program like BalanceLog
to track the actual calorie intake. Diligently doing that can make it easier not to overeat.
As for going to the gym, if you can afford it, maybe schedule a session once every week or two with a personal trainer -- some people find that spending money on a trainer makes them feel far more compelled to actually show up at the gym. If you have a friend who will go with you and you can keep each other honest, great.
Try photographing yourself now, and every few weeks as you work out. It's kind of unpleasant to do at first, but over time you'll see the forward progress and that can be a motivator.
Try getting a big wall calendar and marking on it when you successfully go to the gym in some pleasing color. Over time, perhaps the sight of it will motivate you to go so you can mark up more successful visits.
Or, maybe try marking the days you miss in red or something. Be mindful, though, of whether that is actually a positive motivator or just makes you despondent. It's easy to beat yourself up for stuff when really you have to maintain a positive outlook and just use these things as tools.
On days when you had planned to go the gym and don't, take a few minutes to just sit with your thoughts and notice your mental state. Are you feeling something particular that makes you not want to go? Are you especially tired towards the end of the week? Are you getting enough sleep? Are you feeling hopeless or self-denigrating?
Most of the time, we resolve to do something at one point, but then circumstances change -- it's no longer foremost in our thoughts, we get distracted by some other temptation, we feel less energetic, we're just in a different mood. That's the hard part, keeping that diligence and commitment even through changing circumstance.
Mindfulness, mindfulness, mindfulness is what it comes down to, in the end. Only you know what motivates you, and only you can pay attention to your own thoughts and emotions. You've made a positive step, in deciding that this is something you want. Now it's just all sustained hard work figuring out how to stick to it.