I am 23, 15 weeks pregnant.i have lost my appetite.please advice?

Not unusual: Everything changes constantly in pregnancy. That includes appetite. Early on your nauseous. Later on your probably be very hungry. But there is a transition time where the growing baby is not actually requiring very many calories but is starting to change your chemistry and crowd things a bit. Your OB will be monitoring things but if there is a big sudden change call them. Good health.