I would encourage you to keep a written food log. I have seen very few 18 year old males who eat 1250 calories, even when they are not concerned about their health. If you are spot on with that being your calorie total, that would explain much of your problem, you are under eating seriously.
Take the next two weeks and log everything, even liquids. I would have a hard time believing you are eating only 1250 and not losing muscle.