Also, what is your current job?
Another consideration is that you need enough fuel to make your job function--if it is physically demanding you need energy and if it is mentally demanding you need energy to make good decisions.
As far as diet goes the big picture, strategic basic rules are:
1) good protein intake--you are currently doing this so good
2) predictable meal times--your body needs to know when to expect food. The more predictable your meal times the easier your body will eventually let go of fat. This means evenly spaced out meals of approximately equal calories. With shift work there is only so much that can be done, but set a schedule and keep it.
3) Don't skip meals--this goes along with the above point. The less predictable your meal times and calorie intake the more your body will hoard fat. Incidentally this is also a big reason I said not to abruptly change calories by a huge amount in my first post.
4) Never have a meal of ONLY protein. You need healthy fats to run your body--immune system, nervous system, joints, you name it--so if you are going with a low carb approach each meal needs to have healthy fats in at least some amount. (If you were doing a diet with higher carbs this same point applies to that--no matter the diet never have a meal of ONLY protein....like a scoop of protein powder in water. Bad idea)
These are the big picture things. The diets can get complex, and they can add a lot of details, but they are always built on these principles---if a diet is not built on these principles it is very likely it is bullshit or unhealthy.
TRAINING--Training wise the best immediate advice I can give is to be active every day putside of work. Weight training is great, but in your present calorie condition at 900 calories a day I do not believe you can sustain any weight training. 5 lb dumbbells do not count so those you can continue to use now, I am talking about rigorous weight training.
So my best advice is to be active while you raise calories: go for quick walks for 45 minutes, bicycle, find trails and hike them, anything that is not sitting down and watching TV.
To lose fat the biggest factor besides diet is frequency of activity. Your body is inefficient at burning fat, and as with any new skill the way to get better at it is to practice frequently. At this point it does not matter what you do so long as you are doing something that makes you sweat.
As your calories increase you should start seriously weight training, but right now you need to get out of the danger zone first.