WTH is up with my girlfriend?

She wasnt feeling well today in cl because she just got the swine flu vaccination, so I went over to her and sat next to her and told her that I hope she feels better soon and I asked her if she wants to call her mom to get her out of school then ill give her a ride home. She said no and just brushed me off, but then when her friend (who is a guy that tried to get with her before and they madeout before I was dating her) went and talked to her, I don't know what she said but they kept talking. Why would she talk to him but just brush me off? I did not really have much else to say but I stopped even trying to think of things when she was rude to me I dont know why she was. Why is it that she kept talking to him but almost right when I talked to her she was really rude to me about it? What should I do should I go see her at her house after school in 1 1/2 hours or just call her? I dont really want to go over there because what if she doesnt want to see me right now or something and just brushes me off again? If I do talk to her later and she isnt rude, what should I say to try to make her feel better?