First, congrats on losing the weight you have already lost....for your starting weight 10+lbs is nothing to sneeze at.
I have a question for you...how did you determine your goal weight? 57kg is about 125lb...what is your age/height/sex? I would suggest getting your body fat measured and confirming the weight you are shooting for is healthy and realistic.
I don't know if you have taken this into account, but the same running you are doing now is burning fewer calories than when you started. 1. You are propelling less weight down the road and 2. You body has become more efficient...especially since you are doing the same exercise repeatedly. Also, as you have lost weight your BMR is lower. This all means that the same caloric intake that allowed weight loss in the beginning is now all you need to sustain.
Another possible cause of the plateau is that you have lost some muscle mass along the way...which will also decrease your BMR.
My suggestions...for what they are worth...
1. If you have not already, Get your body fat composition measured to determine a good, healthy goal weight. I have used 'Bodpod' but there are plenty of options.
2. Add in some weight training. Maintaining your lean muscle mass while losing weight is key to keeping that BMR working for you. The bigger the muscles, the more calories they burn.
3. Mix in some different exercise. Doing the same thing trains the body to be super efficient...great for performance but not so much if the goal is to burn calories. As a bonus, changing up your activities reduces the risk of injuries. For me, switching up my exercise is much more fun than doing the same thing everyday and has made it a lot easier to maintain a healthy lifestyle.
Male 45, 5'6"
To date - 32.6 lbs down
Start: 20 Oct 2011: 210.2lb
, body fat =35.3%
Original Goal: 20% body fat - achieved 3/1/12
Last weigh-in: 3-May-2012: 177.6
Last body fat measurement: Oct 15,2012: 14.1%
Goal: Maintain < 20% body fat and < 180lb
Days Maintained : 427