I'm glad you are still on track Sesame and brilliant news about the 'sticky' lb goat, bet you are glad to kick that one into touch. Dieting is indeed a confusing game and I think you have to do what works for you. Maybe you've both relaxed a bit and consequently eating less iyswim?
Not 
A few things to pick out from your post, bearing in mind I haven't been doing this long and am no expert. All meant with kindness. And with the caveat that I am a pretty logical person.
Exercise shouldn't exhaust you, (and I do know about this side of things). It should challenge you, fatigue you, feel hard, make you ache the next day etc. But it should also energise you strangely too and motivate you as you will feel so much better for it. It doesn't at the start, it's bloody hard work. You don't reap those benefits for weeks, if not months. First time I went back to running, like I was chain smoking fags, was horrible. That being said, if you are exhausted then I'm wondering if you need to pop to the GP for bloods? Iron levels? Not actually eating enough to sustain the exercise?
Or, if you really dislike what you are doing exercise wise, how about committing to really brisk hours walk every day, or 5 days a week? That's not too much, and being outside will give you positive mental benefits and you will feel like you are doing something good. A new challenge!
If the same 10 lbs are coming off then going back on again, that must mean something isn't working. Just logic there. Can you see what looking back? Being really honest. I don't know you well enough to make suggestions here.
I've had good results the last few weeks. I've eaten less and moved more, much more!!! Plus, I've really 'owned' the goal if that makes sense? I knew that I didn't want to look at any more holiday pictures and be unhappy. And I wanted to run again, simple. I can be very single minded when I want to be, DH would say stubborn. I visualise what Mo Farah or Jess Ennis would say if they thought about sacking off a training session and I get on with it. When I trained properly (was coached by an elite athlete for a time, long story) I had to come up with 3 positive statements about my training each week and stick them on my fridge. Even as simple as 'completed all my training', 'ate well to support the volume', 'nailed the speed session'. It kept me mentally positive, even if it felt strange. I could get pretty negative in races, helped me change my thinking.
Also, in this long winded and well meaning ramble onwards, I've eaten way more calories than most of you guys, mainly between 1800-2000. And had a glass of wine or 2 each night. I can take or leave crisps and chocolate, but enjoy my glass of wine so I chose to keep this as my treat. I look pretty skinny now, but my diet is excellent and it's been done healthily and in conjunction with most of the Jamie Oliver super food stuff. I've never felt deprived and food hasn't taken me over iyswim?
I still think maybe be kind to yourself. Ignore the scales over Christmas. Enjoy. But aim to walk an hour everyday, without fail.
You can do this, I promise. You really can.
I probably sound like a twat, and I am sorry if I do. xx