To me it *does* sound like your confidence could be coming across very differently to your coworkers. Superiority or arrogance, perhaps. I am also curious how long you have worked with these people because if it's more than 2-3 months I imagine some of them know you quite well (?)
OTOH, I suppose it's possible that these people do have some jealousy and/or self-esteem issues. Like you, it's difficult for me at times to deal with people who have low self-esteem or a degree of self-hatred. I am a larger sized woman but I feel comfortable in my own skin, I feel pretty & capable etc. I don't spend a lot of time worrying about who is thinner or prettier than I am because IMHO I'm pretty, smart, funny, etc. Not in a conceited way. But in a confident way. Anyway...when I meet someone who is constantly comparing themselves to others, dislikes people who are thinner/prettier/wealthier, etc...it's hard for me to swallow that attitude. Likewise, I don't have time or patience to really DRAW people out of their little cocoon if they are super shy or insecure. I won't be rude to them but I'm not going to stop and "baby" them...naturally having healthy self-esteem, it's difficult for me to understand sometimes how other people think.
However, I would not just *assume* that people don't like you because you are attractive and confident. Sometimes it's like a self-fulfilling prophecy, kwim? If you expect people to be intimidated by your confidence and being a bit of a "diva"...they probably will be. I strongly believe in that sort of thing. Maybe you are coming across as kind of flippant and again, superior.
BTW I also work for a similar sized nonprofit org. with a similar male to female ratio.