Am I cold and heartless?

Okay well first off, I'm a girl. More of a tomboy, of that helps or whatever. So I've been thinking about this for awhile. Basically, I don't really care for other people. Sure, I have a close-knit group of friends but I have a hard time being nice to other people. I'm always swearing and get pissed off easily. When someone's complaining (like today my friend was complianimg about how her shoulder hurt after running into a wall) I tell them to suck it up and get over it. I don't care how they feel, they should just quit acting like a baby and get on with it! I'm often very sarcastic and don't care about others. I don't really need that much social attention or whatever. I'm not really a people person. Does that mean I'm cold and heartless? If so, how can I change?