Gradual Weight Gain... Can't seem to lose

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Hey Guys. So for over a year I have been trying to lose weight without any success. I used to be 220 pounds in highschool and dropped down to 150 through diet and exercise. Since 19 onwards (I'm 27 now) I maintained a weight between 150-170 depending on various factors. for over a year I've been 185 and seem completely STUCK. I see a personal trainer and track pretty well on myfitness pal. Here are my issues:

- it seems like even one cheat day erases ALL of my progress. Cheats mean: one bad meal (thanksgiving dinner, for example) or around one night a week of not eating a perfect dinner or tracking all of my calories.
- when I start to lose weight, I get excited and think "finally! my Plateau is done"... but then that one day, that one slip up, seems to erase all my hard work.

My exercise is 2 times a week with a trainer and then I go to the gym, do yoga, or take a class 2 other times. the other days I try to go for walks or do something active.

I've been trying to lose this weight for over a year. I was around 170-175 when I got engaged and was unable to get below 185 even for my wedding. Now that the stress of the wedding is done and I'm happily married I still cannot get down from this 185 block. My husband decided he was a little chunky and dieted and EASILY lost 30 pounds in a few months.

I'm really frustrated. I feel like I'm losing this battle. I don't have unrealistic expectations, even losing one pound a week (hell, even a consistent half pound a week) would be AMAZING. My trainer is at a loss for what to do as well, as I eat around 13-1500 calories a day. I even started watching my ratio of carbs/fat/protein and try to eat a good balance.