People seem to dislike me a lot

I notice sometimes when I meet new people they tend to look at me weird and not smile or appear very genuine. I'm a really polite and smiley person even though I'm introverted and a bit quiet. I just always wonder if people act that way because they are nervous or think I'm weird or something. Today I met my brother's girlfriend and she gave me the same kind of look like she thought I looked weird or something. I'm a perfectly normal person and a lot of people tell me I'm really beautiful so I just don't get it. I'm really nice and empathetic yet people tend to not click with me. Ideas?