Sexuality or Disorder?

I am 16 going on 17.I have had a few "relationships" in grade school, then began dating my now current girlfriend. I had always been uncomfortable with my own sexuality and sexual boundaries, but when i realized i had feelings for her, i set them aside. Not too long ago, we began having a more sexual relationship. While she obviously enjoyed it, i wasn't so sure i did. Masturbation had always been very private and very tame; i always remain fully clothed and covered, and completely silent. I also feel uncomfortable afterwords. Needless to say, i am always a bit uncomfortable during physical relations with my girlfriend, although i have asked her never to touch me during sex. During masturbation, i feel a little more comfortable, but i often wonder if its strange that i don't fantasize about my girlfriend, although i do find her attractive in both a physical and mental way. Instead i tend to fantasize about people that do not exist or who are engaging in promiscuous, random, filthy sex, which i find repulsive. I know people do fantasize about things they like or desire during masturbation and sometimes sex, but i neither like nor desire these things. I used to think i was asexual, but does moderately liking masturbation make me not asexual? I also know that an attraction to people with no regards of gender is known as pan-sexuality. But autism also has an affect on sexual attraction, as well as causing an indifference towards sexual encounters. So, am i asexual, pan-sexual, or perhaps even autistic?