Hey

You don't sound like a wallowing old bag, you sound like I did two months ago. The defeatest attitude is something I can relate to, it was my perogative for a long time (and on my bad days still is).
How did I get over it?
I researched calorie counting and found this amazing site called Calorie King (google it) and it helped me stick to my 1500 calorie per day allowance.
To figure out my calorie allowance I went to Michelle Bridges' website and found out my BMI, BMR and had a look at the calorie exercise chart. These things helped me figure out how many calories my body burns per day, just by exisiting, and how to lose 1 kg per week.
Remember the formula for weight loss = calories in (eating) has to be less than calories out (natural burner+exercise).
Once I figured out what I needed to eat and how much exercise I needed to do to lose 1 kg per week and saw how managable it was the motivation came coursing through me like wild fire. Once you see how achievable something is, the "sad bag" syndrome will dissipate

If your like me and find the exercise portion of weight loss especially difficult its very important to find an exercise you enjoy and can stick at. For me its Taekwondo three nights a week and in addition I have also just started the C25k cool runnings programme that will get anyone off the couch and running 5km in nine weeks.
The key to weight loss for me has always been to make it as easy on yourself as possible. No, I don't mean eat chips and sit on the couch, I mean don't do an exercise you hate because you think its what your supposed to do and if you hate brussel sprouts don't feel obligated to eat them because they're perfect for you calorie allowance. Play tennis or eat peas instead. Sustainable changes are key. Think long term, not short term and you'll have realistic, life long goals. You'll not only lose the wight, but you'll gain a lifestyle as well.
I hope this helps and good luck to you