I'm a guy age 17. Sometimes when I'm walking and talking with a lady friend during school, (when other people are around) I find myself getting an erection, not complete, but it's on it's way up. And this is just walking, no contact whatsoever, the discussions are non-sexual. And I don't think of sex at least not in these specific instances. I'm getting erections. It would be embarrassing if people noticed this. How would I prevent getting an erection next time I'm conversing with a lady friend?