In my Opinion
This is the problem
I am writing this because in the space of a week two friends, both very successful "dieters", made similar comments to me. Both had gained weight "this week", one because she had missed a couple of exercise sessions (because of an increased work load) and the other because she had been out three times. You may be sympathising but I think that any regime that does not allow life to intervene cannot be viable in the long-term. At some stage you will get busy, it will be party season. What they both meant was that their usual "control" mechanisms had failed and so they overate. This is what happens when you stay slim by application of stringent plans, rules and willpower alone. Neither of these two would have overeaten if they had listened to their hunger signals. The exerciser would have eaten less to compensate for the reduced activity and the party girl would not have not treated her social events as reasons for eating too much. There is nothing like feeling deprived to make you rebel when the occasion arises.
Eating when you are hungry and stopping when you are full will never let you down.