I am very skinny but i don't gain weight , doctor says it probably because i'm in a growth spurt right now and that's why my metabolism so fast but no matter how much i eat i just don't gain weight at all and sometimes lose weight. what can i do?

If you eat well you should gain weight when you grow up although you still looks skinny. In case of unchanged weight or weight loss at your age without vigorous exercise, i.e. spending more calories than you get in with meals, medical problems such as hyperthyroidism or juvenile diabetes mellitus, etc. should be ruled out.

Consider asking your primary care to order a Sleep Test or refer you to a Sleep MD. The test can be done at home or overnight at a facility. Possibly because of your sleep, you may have an imbalance of growth hormones; too much Leptin (causes weight loss despite increase in calories) and not enough Ghrelin (causes weight gain). Many solutions exist: CPAP, meds, surgery, & airway trained dentist.