Accidental Weight Loss???

Hey all! Something odd has been happening. Let's begin with, I am 5'3" and about 5 months ago I weight around 115 lbs. I didn't feel overweight or anything like that. Sure, I had a little fat on my stomach and thighs, but that's about it. Well anyway, I never started dieting.. changing my eating habits.. working out.. nothing. I don't believe I changed a thing.. Well, now I weigh approximately 99 lbs. and have no clue what I have done. I feel like I look the same (my face seems a bit thinner) but my stomach still has a bit of fat, along with my thighs, but no drastic change. I weighed myself on multiple scales to make sure it just wasn't the scale being weird, and sure enough, I've lost around 16 lbs in roughly 5 months. What could have happened??? I am honestly really scared.