Thank you for your thoughts, Magora and IceCreamKid. I know you two are trying to help, and I really appreciate it!
Magora, maybe you're right. Maybe I focus too much on people who don't like me. I do expect people to not like me, so maybe I should try to change my thinking. You're husband sounds very sweet, though, so I don't see why many wouldn't like him.
IceCreamKid, I also don't enjoy people who act like you have described. I've met people who seemed shy and quiet, like myself, only to find out later on that they have a very harsh personality I didn't mesh with. My personality is more "soft."
I don't tell people I'm not materialistic or give strong opinions in front of people, so I don't think that counts for me. I just mentioned it here because compared to the discussions of most people I listen to, I don't enjoy materialism as much, but is that such a bad thing? I'm okay with materialism, since other people have the full right to be as materialistic as they want, as long as they aren't hurting anyone else. I could disagree with those who are materialistic, but I won't lose respect for them. I really mentioned it because it seems to be a large part of conversations I hear.
I do have some social intelligence, and I can easily see how putting someone down after they bring up something cheerful would be upsetting. If anything, I think I'm sometimes on the receiving end of strong opinions, rather than the reverse. I do tread lightly around other people's feelings, and I've been told I do. I'm also not saying this as a way to brag or because I think this is very true of myself.
I keep many of my strong opinions to myself, and I understand that there are always differences between people. I don't have many strong opinions, actually, since my strongest beliefs and opinions have been challenged and changed throughout my life, but maybe people don't like that? I don't anger easily, and I don't feel a need to fight any opinions I agree with. I agree that someone who does can be annoying sometimes, but I don't think this fits my description either.
Even if someone doesn't have an interest I enjoy, I still try to talk about it with them, and don't try to act like it's unimportant in any way, just so I don't bring them down.
I do stand too close to people sometimes, and then again, I sometimes stand too far away. No one has ever mentioned how close I stand before, so I'm not too sure I have a problem with this. I don't do this on purpose. I'll be in the middle of a conversation and then become aware of my spatial surroundings. It's harder for me to focus on small things like where I'm standing when I'm nervous.
I don't interject myself in conversations often, and I don't get angry often either. I know, it's difficult to tell if I have an accurate description of myself, since I'm already admitting people don't like me.
Something strange did come from this that I'd like to understand. I noticed, IceCreamKid, that you're examples of people you have known who I might be like are rather annoying or angering, even though I haven't shown any signs yet of being like those people. Could this mean that despite my effort to be a polite, kind person, I may actually be the focus of projection by people who think something must be wrong with me? Meaning, when people see I don't act normal or I don't have a lot of friends, they may come up with reasons to believe why I'm not a good person to be around? I'm actually being honest here. You're right though that I should ask people I know about the way I act. I'll try doing that, and see what they say.
Another thing I've learned is that I'm sensitive and sometimes hurt, even though I keep it hidden. This could be affecting the way people treat me.
I ask people here why people don't like me because I'm too scared to ask offline. After all, telling someone that people don't like you is like admitting you must be a terrible person, and I'm terrified of that prospect. Being a nice person is what makes me feel like myself. If someone came up and told me that all this time I was a terrible person to be around, it'd be like the Earth being pulled from under me. Also, I just can't agree that I'm not a nice person because so much of me believes that I am. I put a lot of effort into being kind and understanding. Maybe I'm expecting too much from others, and that no matter how much kindness flows out from me, I shouldn't expect any in return because kindness should be a gift, and not a trade.
Thank you so much for your replies, though

. I'd like to hear more insights on this, if anyone has something else to add.