It isn't hard to lose weight.
It is hard to realize that you are worth making better decisions regarding your health. Repeat after me, "I am worth it" before you reach for the pizza, the ice cream.
When you say diet week what do you mean? Is it restrictive with a lot of rules that a normal, sane person could never follow and adopt for a lifetime? Or, does it incorporate a wide variety of food choices and regular eating intervals so you never really get hungry?
Three things you can do to help keep yourself accountable and motivated:
#1 - Journal what you eat. Write down EVERYTHING you put in your mouth and calculate how many calories it is. That right there is pretty eye-opening. Often, though, if people can visualize how many calories they are overeating then they have a tendency to have a little more restraint. Once you've journaled your caloric intake for a while and are used to it, you may find yourself planning out your meals for the day (also smart), so that you know if you have wiggle room for a handful of chips and a tiny bit of guacamole instead of bingeing on them.
#2 - Weigh yourself once a week after you've started journaling. Seeing an actual change in your weight can be a huge motivating factor in continuing on your nutrition plan. Pick one day of the week and weigh yourself first thing in the morning. Do NOT weigh yourself on the other days. Log your weight so you can see your progress. (If you'd like to take it a step farther, get a home blood pressure machine - inexpensive at like CVS or Walgreens - and start taking your blood pressure on a daily basis. It's another way to gain objective data in determining the good that your nutrition plan is doing.)
#3 - Reward, reward, reward! My favorite? I get one dark chocolate Hershey's kiss a day (the dark chocolate has flavanoids that actually help lower cholesterol and it gives my sweet tooth a little boost without wasting a bunch of calories). If you reach your weekly goal (about 1-2 pounds per week) then reward yourself with something tangible: a movie, a pedicure, a new workout shirt, a new Nalgene or stainless steel water bottle.
It may be helpful to create a menu for the week and stick to it. That way you won't fall into the trap of "I don't know what to make for dinner so we're having McDonald's." Pack your lunch. Prepare your breakfast the night before (do you like oatmeal? Put 1 cup of steel cut oats and 4 cups of water in a crock pot overnight on low and all you have to do is dish it out. Throw in some blueberries - great antioxidant - and some pecans or walnuts and you've got a delicious, healthy, filling breakfast. Want to be more adventurous? Add a little wheat germ or ground flaxseed for some Omega-3 fatty acid goodness!)
Write out goals for the week. Do your shopping for the week. Designate Sunday as a meal prep day. Pack a cooler/lunchbox for work every day, including all your snacks so you aren't tempted to run to the vending machine.
Good luck to you! Feel free to PM if you have other questions.