I've had the same trouble last few months and I'm 11 months post-op. I didn't loose for 2 months + gained 10lbs. Today is my first day to track my food again and even get support from other posts. I was glad to read a post similar to my situation so I know these episodes do happen to other people even after surgery. (I really thought there was no way I could gain weight quickly again after surgery even though classes & DR said it's possible...well it's true) I got slack on measuring my food and just eyeballing it and I'm sure I prob under estimated calories and protein. I stopped tracking my food daily so I didn't know exactly how much protein I actually ate. And also stopped exercising 4 x a week and just went once or not at all. On top of all that, I had left over Halloween candy and snacked on "mini size" candy here and there. Never counted calories but I bet it was a a lot. Then I said what is wrong because I can't eat much food so I've got to continue to loose weight. But, I was wrong after A quick call to my dietician at DR office and after talking, I realized that I still need to track & measure all food daily (making sure you are getting 60-80g protein), drink 64oz water + exercising at least 3x a week. It sounds like simple ideas but hard to implement daily and correctly.
I'm taking inventory on what issue getting in the way of me not exercising enough. Solution: just exercise 10 mins 3x a day which will equal 30 mins at the end of the day. With my food, make sure I'm getting enough protein and don't graze. I'm just going back to the basics: track, measure, protein, water, vitamins, exercise that you will start loosing weight again.