How can I loose the weight ?

Hello, I am 19 years old and I've been dieting since i was 15 years old. I mean , from very beginning I was on strict diet , in one month I lost 12 kilos , but due to the health problems I had to gain the weight , otherwise I wouldn't be able to recover. So I did it, but the problem is that I have gained too much during the 4 years, so right now I want to loose the weight ina healthy way, so I am on a diet , training for 1 hour everyday and swimming every day. How much can I loos the weight until 9th July if my daily calorie intake is around 1200 -1300 calories ? Thanks