What is this called?

I was at work earlier today and whenever I thought about my boyfriend and I having sex I would get this feeling in me that felt like that butterfly feeling in your stomach but it was lower. Usually my friends and say your ovaries are shaking. I usually just say "oh, my ovaries". This feeling sometimes makes me bend over a little, its not in a bad way or feeling, I just wondered what it was called to get that aroused feeling. And why exactly. Lets just say, if I was a guy, I would have had a boner lol