Hi Andrew, a couple things:
1) You aren't on a no carb diet, you are eating mushrooms! Mushrooms have carbs
2) Are you trying to follow Atkins? If so, your vegetable intake needs to reach 3 cups per day of acceptable vegetables.
3) No, your weight loss will not remain that fast. The first week on a low-carb diet is mostly water. The second week you will see it slow down... Then even more weeks 3-4 as your body continued to try to figure out what you're doing to it! By week 5 or so, your weight loss *should* resume an okay pace of 2lb or so per week. This is a general pattern, not everyone follows it, but it's good to keep your expectations reasonable.
Finally, it's a good idea to think about lessening your dietary restrictions over time, to make it more sustainable. You can't live on four foods. You need variety for nutrients and fiber and sanity
That is why if you are following Atkins, after the first two weeks you gradually add back in other food groups including dairy, nuts, and berries, while still losing. Something to think about, anyway! Good luck!