900cal a day is too little, even without accounting for the running you do. You're putting your body into starvation mode and so will stay the same weight, as your body is hanging onto every available calorie and slowing your metabolism down to conserve energy. Up your cals to 1,200 but keep it healthy natural non-processed food, with plenty of lean proteins and fresh veg and fruit, with healthy fat like nuts and avocado. How much weight are you wanting to lose? Are you drinking half your bodyweight pounds in ounces of water a day? (i.e. if you weigh 140lb (10stone), drink 70oz water; about 4.5pints).
Well i weigh 10st 8 and wanting to lose just over a stone, ive increased my calories to 1300 a day, i eat porridge for breakfast and maybe il have a pkt of cous cous for lunch and sometimnes a baked potato for my late meal, i do drink at least 3 pints of water a day too
There are some general measures which can help you lose weight in a healthy way without any side effects like calculate your BMR (basal metabolic rate), keep a strict watch on your calorie intake, change of diet completely to high fibre, high protein diet, drinking plenty of water before and after meal which helps in proper digestion and prevent you from overeating and exercising (walking, cycling or swimming) to burn your extra calories and keep your heart healthy. In addition to the diet, you can join a gym as well and follow a comprehensive fitness regimen with your trainer which will help you more.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I would have to agree that your caloric intake is too low and body is in starvation mode, very dangerous. What works for me is 1200-1400 calories per day with about 800-1000 calorie burn from exercise per day. I typically do 60-70 minutes of cardio 6 days a week and then 3-4 days of weight training per week. The days I do weights I burn about 1000 calories per day. I focus really heavily on eating the right nutrients. In this medHealth iPhone app I track everything I consume and burn and breaks down the nutrients such as carbs fat and protein. It is important to have a correct balance of those three mcro nutrients. I target roughly and one third split between the three of them. It is hard bit works. I spent 1 yer with only loosing 10 pounds previously without following this method, but over te past 4 weeks I have lost 18 pounds of fat and the amount of weight I can lift has almost increased by 25%. It works for me, maybe it will work for you too.