Skinny, generally consider myself healthy. how do i start digging more into why i always stay skinny?

Lucky you!: Ninety percent of humankind would do anything to be writing this question. If you're a "she", this may well be your natural body type. If your body works like a healthy woman's, be happy with what you have. If you're a "he", serious resistance training and creatine while you watch what you eat will add muscle. Don't compare yourself to the "perfect" bodies in online fantasy sites.