You need to find something that isn't visible and is more long term to motivate you, because weight loss doesn't happen after just a short period of eating well, and it's easy to keep "cheating" and tell yourself you'll just get back on the wagon tomorrow.
I don't need to lose weight and do paleo for my health, but this still works. I remind myself that weight gain and health damage are cumulative and slow to develop. People gain weight (often) at a rate of a few grams a day. They don't wake up feeling exhausted all the time with aching joints, their health deteriorates slowly until they don't remember what it's like to feel vibrant and healthy every day.
I think about the fact that every choice I make is a step in either that direction, or in the opposite one, towards good health. Do I want to find myself at fifty and already in poor health or do I want to stay healthy and avoid creeping weight gain when I get older?
More practically, this is what I did when I was switching to paleo: get a calender and put it somewhere you can't avoid looking at it. Decide that you aren't going to eat X food (bread, sugar, whatever) for a certain length of time. Say just 2 weeks, even. Cross those days off in red. Tell yourself that you can have that food at the end of the 2 weeks, if you still want it. If you can't make it, and eat that food, black out the X on that calender day. For me, there was something really powerful about not wanting to look at the broken chain of X's and feeling like a failure that allowed me to avoid the food without much thought.
At the end of the two week period, tell yourself you can go 10 more days. Cross those out.
Rinse and repeat until you don't think about the food anymore. It might take months but eventually it will happen.
I guess it's mental trickery and it might not work for everyone but for me it was extremely effective.