On the positive side, you seem to be having an immersive experience so far, which is great - it's the whole reason you're there. Now you need to step it up a notch, and stop eating like a tourist. You're not on vacation. You live there. You wouldn't subsist on street/fast food at home - so don't do it there.

Eat like your hosts. It's gonna be a little weird - with the cold cuts for breakfast and drinking yoghurt and cabbage 11 ways, and albino asparagus, and things that have no earthly business being pickled, but just go with it. Just mind the potatoes and the fried meats/sausages, cause they are everywhere. Default to half-servings on these while you're getting a handle on things. Don't have seconds. You can try everything without over-indulging.

Walking: Good job, keep it up. Walk faster. This is good exercise - think of it as exercise. No stopping at the pretzel cart in the middle of your workout. While you're out and about, notice the restaurants. Look at what people are eating, and how much. German food is famously calorie-dense, but the portions are generally way smaller.

Beer: You like beer? Awesome. You're in the land of beer. Be discerning. Appreciate it. Savor it. 1 drink/hour. Don't sully your palette with bar foods. Also remember: a pint of beer's got 200 calories. You want to go out drinking? You need to plan for that when you're eating earlier in the day.

Adopt healthy habits, but try not to think too much about your body. You're not a freak, and it's not a culture where people are going to call attention to you for being big. There are plenty of fat people in Germany. In terms of % of the population, the obesity problem there is just as bad as here. So yeah, okay. In your group, you're the Fat American. Ha, ha, hnng. The pertinent part is that you're working on correcting that. You can still be terrific and fun and sociable, and not miss out on anything in the meantime.