(Another low carber here). This may be way off but are you eating because you are hungry? Lots of people say that eat because they were bored, or tired, but looking back I was actually hungry, all the time, even after large meals I could still eat so would always end up hitting the snack food. Watching my portion sizes made it worse because then regularly I'd go off the rails and usually on food that was more damaging to fill up on.
I would also eat covertly (and cake/ chocolate etc are great foods for doing this as you can nosh them quickly and easily hide the evidence) and like you, plan to eat when others were away so I wouldn't be monitored. I couldn't understand how everyone else could just stop at regular healthy meals - I needed this stuff and it was delicious.
What I found worked for me was the amount of protein you have on the low carb diets - I did the dukan which restricts you to protein only for the few days at the start but you can have unlimited amounts.
And I did. I gorged. I tested the concept of "unlimited" to it's limits. For about 4 days solid. And it felt great because for the first time in ages I was allowed to eat almost non-stop. I felt full. On the fifth day I noticed I hadn't eaten as much, this happened again on the next day. about once every 10 days I'd get "the hunger" again and pig out on just protein. The weight loss was wonderful but not having to hide my eating was what sold the diet to me and kept me on it.
I've lost the weight I needed to but what has really made the difference is that I am now no longer hungry so nothing drives me to the snacks. I still eat (and enjoy!) all the bad foods I did before but I think first "am I hungry?" and if so I have protein to completely fill up on first (leads to some odd combinations - we'll have leftover tiramisu in the fridge from having people for dinner the night before and I'll end up eating 2 boiled eggs, a salmon fillet, a pot of no-fat greek yogurt and a packet of Crabsticks first to kill the hunger that would otherwise make me eat the whole thing and follow it with biscuits, chocolate etc.)