Congrats on trying and posting here when you get stuck, linus. You're doing the right things!
Maybe try looking at eating in a different light. Instead of thinking about going on (and inevitably off) a diet, think about making a commitment to a healthy lifestyle. That means you do the best you can all of the time, but it also means that if you have a piece of cake at a party, it's okay. You enjoy it, then continue with your healthy lifestyle the very next minute. Maybe you exercise a little more that day to make up for it.
I think the key is not depriving yourself and not using "all or nothing" thinking. Think about this: if you got a flat tire in your car, you wouldn't fix it by slashing the other three, would you? So should be the case with your healthy lifestyle. If you mess up and have too many calories or fat one day, you wouldn't fix it by eating terrible foods the next day, right? Get back to your healthy eating right away and keep on keepin on!
Maybe you need a little variety with what you're eating? Instead of turkey sandwiches over and over, try low fat cottage cheese with vegetables one day. Try a healthy nut butter sandwich with reduced sugar jelly. Try a salad with all the fresh produce you can find!
As for your appetite being a roller coaster, make sure you're getting enough fiber, protein, and healthy fats. If you're eating lots of simple carbs, that can make you more hungry. Also, try eating small meals or a snack every 3-4 hours so that you don't get too hungry and overeat.
Best of luck! You can do it!!!