It makes me really sad to read that you feel you need punishment for being fat - I've been there. For so many years. And using that as motivation to lose weight never worked. Because who can sustain the motivation to punish themselves continuously?! No-one! Food shouldn't be a punishment or a reward, it's fuel.

What seems to have worked for me this time (almost 6 months in, 47lb down) is seeing healthy eating as a way to take care of my body, almost like a parent would help their child with their eating. My body is like a kid - "pizza for breakfast!! Chocolate for dinner!" but rather than trying to tell myself "NO DINNER FOR YOU", it's taking an approach of "well why don't we have something healthy and in a reasonable portion first. If we're still hungry afterwards, we can have some more, or a portion-controlled treat for dessert". 80% of the time, the healthy portion is enough, 20% of the time I have something extra.

Calorie counting (using food scales for solid foods, tablespoons etc for liquids, logging everything on MyFitnessPal) has been an amazing way for me to control my portions and ensure that even on days when I do have that little treat after dinner, I'm eating less than what my body burns each day.

If you tend to graze throughout the day and feel restricted if you go long periods without eating, find some lower-calorie and/or portion controlled snacks that you can have in your bag. I almost always have Light Babybels (66cal) and Muller Light chocolate puddings (95cal) in the fridge, and some kind of baked crisps/chips (100-120cal) in the cupboard. What works for other people (e.g. only eating one meal a day) might not work for you - and that's OK. Figure out what does work for you.