Hey Lucy,
Good job hanging on so long. I'd say go for it. Try increasing your calories and see if it works. In all seriousness, the plan you describe would/should make you the calorie counter poster child. From what you describe, you are doing every single thing possible and correctly to lose weight, but for some reason you are not. You say that past lab work show you don't have health issues, and if you are doing everything you say you are it is very baffling to me, (and I'm sure it would be to any health care professional) that you are not losing weight. I don't see any other choice than to try raising your calories. Just remember it is possible for your weight to go up a few pounds at first just from weight of the extra food in your colon.
I would also like to mention though, that some times weight loss happens in what we call around here, "whooshes". lol Your whoosh might be right around the corner. Tomorrow you might decide to eat 1800 calories and the next day you might be down 4 pounds all of a sudden. Please know that eating more calories didn't necessarily create the big drop overnight, but more probable it was just the time you body decided to dump the extra fluid and give you a new scale reading.
Keep us updated on your progress.