A few years ago I discovered that when I lie on my back on the floor, hold my legs straight and move them up and down I eventually get an orgasm. Normally I only need to move my legs up and down 20-40 times, sometimes longer but I always get an orgasm from doing it.

How can this be? And how do I know if it's a clitoral or vaginal orgasm? I've never managed to get an orgasm from masturbating and I haven't had sex yet so I don't know how it's supposed to feel but I'm sure it's an orgasm cause my legs start shaking and it feels really good.