OP, how old are you?
You sound a lot like me. I eat one meal a day (Not for the sake of a diet, but just because it's the way I've always been, and I don't get hungry during the day). I eat less calories than you. Lately, I can't lose weight no matter hat I do.
Up until my mid 30's, I never even had to give weight so much as a thought. I was always slim.
Late 30's I started gaining a little- not fat or anything- just heavier than what I always had been.
Late 40's....I woke up weighing 228 one day! (Had always been 170-180 since high-school).
I started taking weight loss seriously, and got back down to a maintainable 170...for a year or so. Now, at 55, no matter what I do, I just keep gaining- back up to 197- tried everything- it just seems to make no difference. I've always had a slow metabolism.....and lately I think it's even slower. It's unfathomable as to where it's coming from- all I drink are water and tea; and I eat good simple cooked-from-scratch food- I NEVER eat out.
I think it's just the age. Maybe we need it. When I was keeping myself down in the low 170's, I was getting pretty weak. I actually have more strength and stamina being overweight.
Oh, and the really absurd thing? I was a vegetarian (almost a vegan, really) for 15 years, and it was at the end of that period that I emerged weighing the 228- the most I've ever weighed.
Could imagine if I were to eat junk?!!!!