If guys rarely talk to me, does that mean I'm ugly?

I am quiet and usually by myself. I dress very casually (t-shirt/jeans). Once in a blue moon a guy will hit on me, but it's not a super common thing. I never thought I was ugly at all, although I'm not stunningly gorgeous or anything, but could I be wrong? While I'm not the most outgoing person, I do try to come across as generous, friendly, and laid back. I don't act extremely girly, and my interests are more masculine than feminine. I thought maybe guys thought I looked like I wasn't easy to talk to or something because I'm not bubbly and talkative all the time, but I've been told that if I were truly attractive, guys would approach me no matter what. Is this true?