Why am i losing weight?!

Im 18 years old, 5'9 ish and been that was for about 3 or 4 years now, and i have about a 3000 calorie diet weighed about 130, and i almost never exercise. Ive lost about 5-10 pounds in the last 3 weeks and my coller bone and hip bones are starting to stick out. what might have causeed it??