Why am I so horny all the time?

I am a 16, almost 17 year old girl who's single and lately I've been noticing that I've been feeling really horny a lot lately and having a craving to have sex and lots of sexual urges. I really don't know why... And it's always so random, like at the most random moments. when I'm in my bed, all I think about is sex, and I've been watching a lot of porn, masturbating, and looking up a lot of stories questions and information about sex. It's driving me crazy and I feel like I can't get rid of or crave my sexual feelings. Is this normal? What's causing me to feel so horny, and what should I do to feel less like this? I don't mind being in a romantic sexy mood sometimes, but it's too much!! please help :( thanks!