My friend thinks that I am mad at her but I can honestly say that I am not!?

So I had my friend over this weekend and it was awesome. We had a great time. I'm moving away though, so lately she's been hanging out with other people and honestly I am okay with that. But lately she seems to be ignoring me and we only had a sleepover...3 nights ago! She is hanging out with the popular clique, and she says that she thinks that I'm mad at her. I don't want to be gloomy or sad. I've just been having a hard time with exams and that stuff coming up. She keeps asking me if I'm okay. We used to tell each other everything, and up until two days ago, we did. I'm so confused..What do I do to make her know that I am not mad at her. I have already explained this and told her that I am not but she doesn't believe me. I don't want to be a gloomy person, in fact, I'm pretty optimistic. I'm just moving and have nobody to talk to, so it is understandable that I am not too happy, right?? I don't know what to do. How do I get things back to normal?