not losing weight on keto

If you can't eat enough calories on keto you shouldn't be doing keto.
Long term you're looking at severe metabolic adaptation. Unless you want to maintain at 900 calories eat more carbs.

QFT!

I don't think it's wise to undertake a keto diet if you don't know exactly what you're doing and it sounds like you are not sure. There can be side effects from doing a keto diet incorrectly (and personally I'm not convinved that there aren't potenital problems even when you do it right, but that's a whole 'nother discussion), including becoming seriously dehydrated and electrolyte-deficient. And 900 calories a day isn't enough for anybody in a day. In ketosis, you have to support your body with plenty of protein and fat in order to make up for the lack of carbs, which are the preferential fuel for the body. 900 calories is not enough protein and fat to provide your body with energy. And, if you aren't getting around 1200 calories a day, it is likely that you aren't getting enough food for proper nourishment either. My personal advice would be to try to follow a more traditional eating plan focused on healthy foods, exercise, and calorie deficit before undertaking a keto diet. But if you are set on trying this out, my other advice is to make sure that you have done your homework before you continue on.

What is your height, weight, and weight loss goal? Have you spoken to your doctor before starting this diet? Are you following a specific program or did you just pick low carb and start eating <20g a day to see if it would work? All of these questions are important in figuring out what you should be doing. If you're dead set on doing this style of diet, I strongly recommend that you get your doctor's approval and advice on how much you should be eating to lose weight. If you are dead set on not going to a doctor, I strongly recommend that you get some suggestions from the keto dieters here about a good plan to follow and some websites to read and then go and do the serious reading about how the diet is supposed to work (and why it works and how to make sure you are doing it safetly) and actually follow the plan. People do succeed on keto diets, some of them long term and many not so long term, but I think you will have better luck and a safer diet if you get some guidance.

Also, in regards to calorie intake, the people who should ever legitimtately be eating less than 1200 calories per day are few and far between. If you are worried about your food intake, use a tool like MFP to calculate your calorie intake for your height and weight and then use the custom setting to change your carbs, protein, and fat to your keto diet plan and then follow it. Whether you are losing weight or not, you need to eat enough to be properly nourished. And, unless you are an extremely petite and already skinny girl (or have a medical condition), you can still lose weight eating more than 1200 calories a day.