Losing weight and regaining it over and over is called "Yo-Yo" dieting just like your situation.
Tips to Stop the Yo-Yo Cycle
1. Soothe Without Food
2. Change Your Goals
3. Scale Back
4. Share Your Meals
1 pound is equal to 3500 calories so to gain or lose a pound we have to either ingest 3500 more than we burn off or burn off 3500 calories more than we ingest. That would have to be one huge treat meal to gain back 2 pounds. Sometimes knowing that info can help u adjust. What's ur exercise routine look like? How many calories are u eating other days?
No, it's not normal to put on that much weight from treat or cheat meal. Apparently, your "treat" meal is too large or you're eating all the wrong things. While a treat or "cheat" meal is sometimes, recommended or some people say it's okay, if you have to fight all week long to get rid of the weight you gain from it, you have to ask yourself if it's really worth it.
Personally, I don't think a treat meal, every week is a good thing. I think if you're depriving yourself of the foods you like, your "diet" isn't going to last very long anyway. You should be able to eat most of the foods you like, by keeping the portions small so you aren't overeating to start with - by doing that, you don't have to cheat or treat yourself. You're satisfied with what you're eating to begin with.
Almost every "comfort" food has a leaned down version that tastes just as good and in some cases, better, than the high fat version. You just have to look for them.