Natural body weight?

I shouldn't be bummed about a mere 100g gain. But it got me thinking...

I remember reading somewhere, researchers/experts/nutritionist whoever it was, saying that each of us has an ideal weight. A weight our body is just naturally supposed to be. When you try to go below this weight, it is hard to stay below, hard to maintain and requires too much work to stay there. Your body wants to go back to its natural weight and will get back there.
What is that weight? How do you know what that weight is? Would this natural weight be in your healthy BMI?

I haven't weighed this weight for an incredibly long time. I stopped weighing myself when I was in year 10, health. We had to weigh ourselves...no...other people had to weigh you. How f'n horrible for someone who knows they are overweight. To have someone else weigh you, and call it out to the recorder and of course EVERYONE can hear! From memory, in year 10 1990- 14 years old, I weighed high 70s.

14 years later, I had to be weighed again, I went in to see the anesthetist for my knee reconstruction. I cried when I saw 110kg. He sympathised with me. He reassured me that when you do your knee, you CAN'T exercise so of course you are going to put on weight. You can't control it. I did my knee in 2000, well partially...I tore it. Then in 2002 I ripped it apart. No sport, no exercise possible. But come on: I was always fat. I was fat before my injury, I was fat before my year 10 weigh in. Infact I was always obese.

004= knee reconstruction. Immediately after, my weight went higher. I think around 115kg. i never weighed myself. I joined the gym to help with my recovery. over 18 months of just focusing on exercising, i got down to about 95kg. That was the smallest i had been since maybe 1998. That was the smallest my husband had ever seen me. We got married in 2004, so he only knew me 100kg+.
Then I quit the gym as we moved house and got a bigger mortgage, and then fell pregnant. I was 101kg when I first weighed in at 10weeks pregnant.
That was in 2007.
Child born, I weighed 104kg.
yes only 3kg put on during my pregnancy...one good thing about vomiting for 39weeks!

Started WW November 2009, weighing 107.7kg. The first time I had weighed since giving birth.

The first 20kg really flew off. They were easy to lose.
I know everyone struggles as they get closer to goal so I shouldn't see myself as being the only one who is going through this. But most people have a goal weight that is in their Healthy BMI. WW sets it in there.
My leader set mine above my healthy BMI. 77 kg. BMI approx 27. I should have a goal weight of 72kg to get me to healthy.

but I am struggling 10kg out from HEALTHY BMI, that is NOT close to goal! Is it possible my natural body weight is meant to be overweight?
My dr once told me that I should aim to get to 72kg. But I will be happy somewhere between 72 - 85kg. That is a massive difference.
But is he right? Is 81/82 my happy zone? My natural zone?
Not being smaller then this, I just don't know.
I would like to think not...but...can you fight what your body wants?
What if 77kg is unattainable, yet i am wanting 72kg?

How do you know your natural body weight?
And how do I jolt my body to just bloody lose this weight! I would so dearly love to get to the 70s. or even to my 25% (80.7kg). It would be so nice!
I know I am sick of the up/down results I keep getting each week. I would happily take 100g LOSS each week. But i am up one week, down one week, up, down, up, down...i would prefer small losses to anything else!

I am sure if there were answers, we would all be at goal weight! so i guess this is more rhetorical then anything!

But, for now while my questions go unanswered...I have made a promise to myself that tomorrow I am leaving work at 4pm to go to Jacob's Ladder in Perth. It is my first go at it, and I want to do 5 sets. It is 43 m long, with just under 300 steps. 

Jacob's Ladder: Kings Park Perth

300 steps up, 300 steps down...5 x...just like my weight...hopefully that will jolt the body...i can take it as punishment for my up/down journey the past 4 months...and because I never want to do that again, I will do everything to stay off that ladder which means LOSE LOSE LOSE! or i see it as a training session for the city to surf, and i am doing it because of training, not to impact on my weight loss. Therefore I must put my heart and soul into the plan, doing the program, living the program, but I do feel I do that mostly!
aaargh...the mostly kills it doesn't it?!