I am gaining weight on Atkins!?

I usually start my day with 5 grams of carbs in milk 6 grams in splenda and two in coffee. Then tuna and mayo and onions and sprinkle cheese the first two meals of the day. Snack on cheese. Maybe just a steak for dinner. This only adds up to like 25 carbs. I drink plenty only water. I do drink vodka. Is this why?