Average day would be Greek yogurt for breakfast or noting if I'm not hungry. Lunch 3 slices of streaky bacon and 1 fried egg. Dinner steak or pork chop with egg and mushrooms sautéed in butter and maybe some peanuts later if I'm Pekish
If the only veg I was eating every day was mushrooms (virtually nil fibre) then I would be seriously constipated - and that could easily explain the weight gain.
Personally, I probably eat 500+ g of veg and 50-100g berries a day.
On a day when I eat a green smoothie, I have that amount
by the end of lunch, then eat
another 300g with my evening meal.
Eating low carb does NOT mean eating only fat and protein.
It is an opportunity to eat masses of filling, satisfying salad, veg and a bit of fruit, resulting in (IMHO) a far more nutritious and varied diet than when half the bulk is taken up with nutrient deficient carby pap.