I’m 16 almost 17 and my weight is kind of all over the place. It can go anywhere from 120lb to 145lb (I’m 5’4” if that helps/matters). It doesn’t seem to matter when I’m exercising or not. I’m not losing muscle mass, but sometimes I won’t work out for a while and my weight will drop to near 120lb and other times it just spikes up for no rhyme or reason up to 145lb (I’ve lost 7lb in a day before for no reason). Is it just my metabolism or should I be concerned?