suddenly lost weight??

hey this is my first post on here so I’m not exactly sure how this works but it seems like the perfect place to ask for some advice

I’m 16 and have always been quite slim but suddenly at the end of last summer I dropped basically any fat I did have on me, there hadn’t been any big changes in my life that would cause it and doctors couldn’t find any cause either. Past few months I’ve been stuffing my face and obsessively drinking protein shakes and trying to build muscle at the gym but nothing’s working. If anyone has any tips I’d really appreciate it because I’ve been feeling pretty miserable about the whole thing.

(Me in August 2018)

(Me now)

You might laugh cause it’s a small difference but I’ve always wanted to gain weight and b less scrawny so the fact I’m inexplicably loosing weight is infuriating. Thanks if you took the time to read all that! (Also I have bowed legs hence why they’re curved)