Lip Lift; Am I a candidate? Upper Lip Problem? (photo)

I am 17 year old female, who has quite full and youthful lips, both upper and lower lip. When I smile the upper teeth shows, but when I let the lips relax and vaguely open my mouth, my upper teeth does not show at all, the upper lip just hangs over the teeth. Is this normal? + is this a sign of weak upper lip muscles?