Hello, I am new at this. I started on Jan 6, 2019. So far I have lost 26 Lbs, so must be doing something right 
My problem is I am allowed 1200 Calories, but I am rarely hitting that target in any given day. I usually am around the 900 Calories per day mark because I just don’t have an appetite anymore.
Any suggestions anyone???
If you are eating only when hungry and stopping when no longer hungry, don’t worry about it. That’s listening to your body, not restricting calories. (In other words, it’s your body, not you, deciding on your caloric intake.) On the other hand, if you were hungry all the time, I’d be urging you to eat more.
So congratulations, and keep ketoing on! 
You probably have reached a point of fat adaptation which means your body fat is being used to supplement caloric deficit so just go with it and don’t worry about how many calories you are eating.
I went a solid month on 1200 calories per day but I felt great and I just wasn’t that hungry. I ate when I was hungry and I stopped when I was full and it taught me a valuable lesson about understanding and trusting my hunger.
You have lost 26 pounds in just over 50 days so you are not exactly doing keto.
900 calories a day for 50 days is a very low calorie diet and your body will probably try to adjust to that lower rate by slowing metabolism. From what I have read, this happens between 3 and 6 months. It might be that sometime after the 3 month mark, weight will stop coming off or even go up - and cutting calories more won’t help much (instead you will get colder, weaker, grow less hair etc.). It is the classic low calorie conundrum.
To avoid this, you could try throwing in weeks of intentional over feeding - make sure your body doesn’t slow down. You could also do something as simple as alternate-day-fasting. Eat nothing on one day - then a lot on the next (by which time you should be naturally hungry enough to get down 2400 calories).
The thing to keep in mind is that fasting - extended fasting and it’s adaptations - can go on until all of your weight is gone. IF (better thought of at TRF - Time Restricted Feeding) can help but if you are still at 900 a day - it will stop helping at some point. Keto (with bouts of higher and lower calorie intake) and it’s hormonal changes can go on until your weight settles at where it thinks it should naturally be.
But, the middle-range (being keto or any other WOE/diet) of continual calorie restriction will drop weight quickly, might make the body slow and could lead to a bounce.
(Of course, it depends on your current and goal weight - but you mentioned you were at 33% less calories than you think you need.)
hi, are you including the calories from the fat lost in you daily intake? Losing a pound a week (3,500 cals of fat) is supplying your system with approximately 500 cals/day. That plus the 900 you eat is 1,400/day. Actually 200 over your 1,200 target. If it were me, I would not worry and keep on ketoing on. Your progress is impressive.