I think you have to gauge the person. Some girls really don't care, and won't ask. Others are really sensitive and wish to know.
Personally, being 25, I've gone through spells. Like most. At times it's a different one each week for 2 months, then bone dry for 3/4 months. Then 1 for say 4 months, then dry again. Being social, active and having a car within a car group full of 18 - 19 yr olds, girls was never really an issue. A decent one was haha.. That came later in life. Now I'm like mast3r - 1/2 twice a month if I'm lucky.