What do I do? I think Ive fallen for my close friend?

Recently, Ive had some different feelings to a friend of mine of the same sex. I feel like I want to be more than friends with her. Ive never felt this way with other girls, but have had feelings for guys.
Its really weird. Each time I see that friend, I get this really weird feeling, like butterflies in my stomach, and like i want to be more than friends with her i guess. Im sure she is straight and doesnt feel the same about me. I dont know. its just really strange for me. I really dont know if I really am a lesbian. Im really confused with myself, especially since I have had the same feelings for a guy as well. help?