Situps More Than Just Tummy Toning

I don't know if this works for anyone else but when I was a kid I used to like to do situps to make my stomach flatter. One day I was doing them and noticed how it kind of felt weird between my legs but didn't think anything of it.

Well, a couple years later in gym class we're doing physical fitness tests and I'm doing situps with another girl counting them, and I got the same feeling again, only this time a lot more intense. It was so strong, I had to stop and tell her I couldn't do anymore situps, when in reality I was worried what would happen if I kept going. Imagine having an orgasm in front of your whole gym class! I think not!

Is this just something that is specific to just me, or do other females experience this as well?