Struggling with Plateau

Hey all, I am struggling with a stall in my weight loss and I'm confused how to proceed and hoping to get some advice and learn from everyone!

Quick background, I went on a general diet and did weight lifting for 3 months and didn't lose any weight (though I'm sure there was some muscle/fat trade off). Then about 2 months ago I switched to a low-carb diet and dusted off my P90X and lost an average of 2lb a week for about 6 weeks, some of which I'm sure was water from lack of glucose. However as of about 2.5 weeks ago my steady losses slowed down and than stopped at 208 lb where they have held steady for about a week and a half now, in fact today I'm up to 209 again. I'm a computer guy and have an excel sheet where I track my statistics based on daily weigh in's first thing in the morning, as well as one for daily food consumed broken down into overall calories and fat/protein/carbs. I eat the same 3 meals every day, no cheat days and consume 1~2 gallons of water a day (normally closer to 1 then 2), about half of which is made up for tea, mainly green tea.

My question is this, am I eating to many calories, aka eating at maintenance or slightly above, or am I not eating enough and my metabolism has slowed down and is now trying to store fat?

I'm 31, 209 lb, 6ft even and I work a desk job (but my desk is adjustable allowing me to stand 50% of the time). I walk my dog 1.3~1.5 miles a day at a decent pace followed by a 60~90 min P90X workout 5 days a week. My calculated BMR is roughly 2000 and my calculated TDEE is roughly 2900~3100. However my Fitbit Charge HR says I'm burning 3500~4000+ (normally around 4000) per day. My daily meals put me at 2400~2600 per day, depending on uncontrollable serving size variation). I upped it from 2100 per day recently due to my high readings from my fitbit, but haven't seen any changes other than about a .3 lb gain per day.

If I go off my fitbit I should eat more to get to a 20% caloric deficit, but they can be inaccurate while my TDEE says I should maintain this caloric intake or even decrease it a little. Any suggestions from anyone? Any way I can be more sure what I should do? Any thoughts or advice is greatly welcome!