I'm a teenage girl and have never been sexually active in any way, but i find myself very "horny" a lot. i can't help it. why is that? is that bad?

This is normal.: Sexuality in teens is a healthy sign that hormones and other physical/mental/emotional components are functioning as they should. "Horny" doesn't stop at 19, either. Healthy sexuality is a life-long condition if overall health is intact. While sexuality varies in intensity (some have more some less), it generally correlates with physical robustness.