Why is it so hard for me to get a girlfriend?

All the girls I ever went out with were the ones that hit on me. I'm extremely shy and dress plainly but not like a geek. My parents who are very religious drove them all away because they weren't what they expected. I'm 20 years old, want a relationship (not necessarily serious marriage wise), and want to lose my virginity really bad. It's been 3 YEARS since my last girlfriend. Even though I have friends I feel like I don't fit in because they have what I don't. My parents are overprotective and try to run my life and I'm trying to find a way to move out on my own. I'm a good looking guy but only about a handful of girls actually hit on me, none recently. All the girls I hit on (which weren't very many) rejected me. I guess it was because I was too shy or something. Yesterday I talked to a girl who works in a store in a mall. I also talked to her a few times before that. I forced myself to be aggressive and wasn't being my real self but it was super effective. The only reason she didn't go out with me was because she already had a boyfriend. I said "You know, I think you're pretty hot." She giggled and then I said "Do you want to go out with me?". Afterward I explained everything to her and asked her how I did and right off the bat she smiled and gave me a thumbs-up. At first I felt great but later on I wondered why I have to completely go against my personality just to stand a chance of getting a girl. I don't think that's right. I'm confused. I thought girls like shy guys and ones who be themselves.