What's causing my weight loss?

I am an 18 year old male, and recently I've noticed my clothes becoming slightly looser one shirt that used to be skin tight now fits normal I haven't weighed myself since fall but then I was around the 280-290 mark. I have had no changes in in my appetite or diet but it appears I'm loosing weight. I do have anxiety and depression and both have been heightened the last few months but not enough for me to stop eating or any thing abnormal from my day to day. I'm not concerned it's a health issue yet because it hasn't been an extremely drastic change my guess is probably 10-20 pounds which is great but I just am not sure how it's happening. Does anyone know what might be causing this?