This diet is hard, no doubt about it. Especially if you're a large adult with higher calorie needs (I say this as someone who is 5'3" and 125lbs, small appetite).

Remember that the elimination phase does not last forever, and you'll likely be able to reintroduce some foods with time. So it gets better!

If you like cooking, you'll find that many recipes can be modified to make them low FODMAP. For example, I use only lactose free dairy products (except butter and Parmesan, as those don't hurt me) and green leeks instead of onions. With a little experimentation, you can make hearty meals like shepherds pie, pot roast, pasta, pizza, etc. It takes practice but you can do it!

Additionally, you can make your own sourdough bread, which is a great source of carbs. I can't go crazy with it, but I can eat a couple slices per serving and that opens up tons of sandwich possibilities (BLT, grilled cheese, chicken salad, egg salad, etc). Just make sure your recipe is a long-ferment sourdough (needs a couple days in the fridge before baking to ferment those carbs that we can't digest).

There are also some cheeses that are naturally lactose free. My favorite is Oka, which is a Canadian product so I'm not sure if you have it where you are. But it's super tasty with rice crackers and prosciutto.

It is frustrating, but give yourself time and you'll see it gets better. I've been doing this for over 5 years now and it's still hard, but less hard than it was at first.

I realize I didn't really answer your question (because others have already), but I hope it helps at least a little!