Calculating TDEE based on daily activity

This seems pretty acurate. I'm female, 47, 5'7", and 171 lbs

It says my BMR: 1506

My TDEE: 2508 Rest days (8 hrs sleep, 6 hrs standing, 10 hrs sitting)

My TDEE: 3424 Workout days (30 mins HIIT, 30 mins weights, 8 hrs sleep, 6 hrs standing, 9 hours sitting)

I ususally eat around 1800 cals every day and have a spike day (3000+ cals) once a week. If I didn't have the spike day, I should probably eat more on my workout days. If anything, I could probably up it to 2000 and still lose weight. When I plateau I will try that.

The problem I'm finding is getting the numbers to balance.
I have hit the dreaded plataeu and I am struggling to get off it, and I am almost at the point of giving up.
I've lost/gained the same 5lbs for the last six months. At first I put it down to the sudden death of my mum but its been a while.
I got a fitbit ultra and discovered even allowing for a 5-10% error margin I am a lot more active than I gave myself credit for, as my work is so varied on a day to day basis I had always put myself down as sendantary, and then added in exercise - I've power walked a half marathon and do an almost weekly timed 5K, plus I do a short but fast cycle to and from work to collect my child every day.
I had assumed that as I had over 80lbs to loose when I started that it would be resonable to set my calorie goal at 1200+ exercise cals. I didn't know about BMR back then.
So having done the research of BMR - I'm 5' 4" 190lb and have a body fat of 37% the averages over three different sites gave me a BMR of 1549. Using that with an activity level of 1.55 gave me an average across the three sites of
TDEE 2350

so I need to eat close to 2350 +/- 100-300 cals for maintence. I worked on the 15% cut as a maximum from TDEE to get net cals of 1997 per day. But having been on that for 4 weeks the scale still isn't shifting.
I have dropped my cals down to 1660 as I dropped my activity level by one.
my fitbit is giving me an average TDEE of 2716 the only additional exercise I add is the cycling as that I know the fitbit is not accurate on, but i am at a loss as to what to do, I have numbers and calculations coming out of my ears and I don't know what to go with.
I know if you look at my diary my food choices are not the best in the world, but I want to get the calories right first and then I can look at changing more of the quality of the food I eat, as it isn't just me I have a family to think about and we don't get home
until 6.30pm so we have 30 minutes to feed the children, do homework etc before they need to be in bed. it will start getting easier to manage as daughter get older and can stay up longer, but as we are up for school between 6-6.30am its a very long day for a 5 year old.

Thanks for any feedback - espeically if I have got my maths wrong somewhere it isn't my strogest subject!!

I'm wondering, has anyone used the weight loss calculator tool on that site using their TDEE and intake to estimate how much they'll lose in a month? And if so has it been accurate?

http://www.health-calc.com/diet/weight-loss-calculator

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