Feeling mean doesn't always mean your being mean. From quite a bit of the stuff you said it's seems that you appreciate your friends and that you are nice person. People can't always be sensitive to other peoples feelings when they them self are having trouble with there own feelings (such as you feeling like you may be being mean). The mood swings could almost certainly be explained by it just a teenage thing a lot of people have mood swings when there teenagers as its all part of growing up blah blah blah . In conclusion it seems to me your intentions are good, your a nice person and your just a going through a stage which is making you feel uneasy.
If you realize how you are to people around you, why not change your behavior? Appeal to your better nature. If you believe you're a good person, then you are! Prove people around you that they are wrong about you! It's not an awkward situation to suddenly change your behavior to people. It notifies people that you're trying to be a better person to everyone from now on. If you believe in the kindness of people, they'll believe in the kindness of you. And trust me, you'll feel it.
Expect great things if you're good and respectful to others. You're never to late : )