Take a look and listen to Steve Phinney a low carb expert MD for some 25years. Pay particular attention to his description of what nutritional ketosis or keto adaptation is, and the description of your body's ability to have ready and easy access to your fat to burn and have plenty of fuel, even if you are only taking in 1200 cals though your mouth. I am not suggesting that you could not or should not eat more calories (I am not a calorie counter). That is up to you.
I would suggest that you slow your expectations down and begin to look at this change as a learning experience that you need to learn very, very well. Radical weight maintainers, of which I am one, are a very rare breed. Only up to 5% of all weight losers of any amount, keep it off. Of the 95% who regain, 50% or more gain it all back plus MORE. This is a very, very common pattern, so common as to be the norm.
Among radical losers, only 1-maybe 3% of us manage to keep it off. Those are heavy odds. They imply to me that something goes wrong ALOT post weight loss; that there is much that is highly unrealistic and poorly understood. One such thing is that a generalized statement can be made that there is "no going back." It is a myth to think that you diet can change much at all post weight loss. This is a strong argument in my opinion to take it more slowly and not drive your calories down too far in the beginning. You are essentially training your body about what energy (food) level to expect. You body will quickly adapt to that depressed calorie level. The beat goes on. It is a lifelong endeavor. Your body becomes more efficient at energy use, your gut bugs become wizards at nutrient extraction and the endocrine system reacts to radical weight loss in such as way as to constantly relate to your brain that you are now starving which leads to HUNGER. There is much to learn. Perhaps start here and look at being ok with slowing down a bit and over time, slowly finding out just exactly what will work for you and most importantly, what you can sustain for the rest of your life.
I am a ketogenic low carber who met initial goal in 2002 after starting in 99 (down from 240lbs to 145-148lbs, who lost additional weight for a current weight of 128-130 in 2010-2011.) ALL low carbrs and low carb paleos start out believing they will progress on the carb curve over time. In my experience, for some FEW people this is true. For many, especially radical losers and those who developed obesity at a young age, carb progression often does NOT work. Or, it works because weight gain happens and techniques like protein sparing modified fasts (to the tune of 500- less than 1000 cals) are used cyclically for a week or two at at a time, to whack the accumulated pounds off, over and over and over. (What this may do, in and of itself, long term, to your metabolism is a subject for another discussion.)
You must become your own objective science project, gathering as much quality information along the way as you can. What you get here will not always be quality information, sometimes because the person giving the information buys into alot of myths of obesity/maintenance and because perhaps their own knowledge base is very limited and they are parroting generic info.
You can do this. And you can maintain your loss. It is possible too that you may need to adjust your goal to what your body settles into as your best sustainable weight rather than an ideal weight that is not sustainable. Until I was able to sufficiently de=stress my life and give up being on call 24 hours and all shiftwork, 130lbs was a totally unsustainable weight for me. My life has changed now and it is quite sustainable. Stress matters too. There are alot of factors that go into this. Check out Arya Sharma's blog for just one for excellent info in many areas.
Welcome, good luck, and hang in there. And perhaps when you ask questions, specifically address them to those who have been in your "shoes"( big losers!) and have successfully lost and MAINTAINED that loss, preferably for 3 years or longer.