I'm guessing either you haven't met someone yet who inspires you to feel those feelings of affection--or else perhaps on some level you have some discomfort and unfamiliarity with people of the female persuasion. I'm not saying you're gay by any means. You may just be in unfamiliar waters. Have you ever had any close female friends?

There's no law that says you have to like girls. There are a heck of a lot of straight guys out walking the planet who don't. Give it time--and work on getting to know some girls as people, not just as objects of attraction. If that doesn't help the situation, it might be time to look at the relationships with, and attitudes toward, the women in your family of origin, the ones who have been the models (mothers, sisters, etc.) for how you feel about the other women out there.