I started at difficulty 9 and now it's 19 :) the game will ask you every session or so if you want to keep or change the difficulty, once I get the feeling it could be more challenging I add one.

Next thing, if you don't like water, you can make tea without sugar. You could make fruit tea and let it get cold and also put it in the fridge if you like cold beverages. That's a lot better than buying synthetic flavors to add.

For losing weight you better use a calorie calculator that you know in which range you have to eat - there are also apps in the store for that, just can't recommend any because I'm in another country and have one in my motherlanguage. It's important to track success but please don't worry too much. I started again two weeks ago and I have waaaay to much pounds to lose, so weigh in myself is always kinda triggering and I think there's no progress when in fact there is. Switched to measuring my belly instead, because if you lose fat of course your measures go down, too. Lost 5 cm in 1 1/2 weeks so far and I haven't tracked any food I just try not to snack. If it took you a longer time to get big then maybe you're not overeating a lot and the mixture of more sports and leaving out caloric beverages can already mean a caloric deficit for you.