Too busy for a relationship?

I've been dating a wonderful girl, but in the last few weeks things have changed. She has been working and studying more, and we barely have time to see each other. I've offered to just accompany her while she works and not bother her, but she says it would just distract her. She hasn't been replying to my messages much (and I only send one or two a day at most, in the hopes to cheer her up and motivate her, just simple things like telling her to work hard or saying I love her) and if she does reply it's really basic, not very thoughtful, like "okay, thanks for your support". Now I understand she really wants to further her career, which I support and probably would be better for us in the future, but it's really bothering me that she has no time for me, and when we see each other, she seems tired, stressed, and not as playful or happy as she used to be. I both worry about her health/happiness and mine. I don't want to break up with her, nor for her to break up with me because of the lack of communication, but I also don't want to stop her from following her heart and working/studying hard to eventually change careers. Any suggestions on what to do in this situation?

MMM3 - I assume you have tried talking to her and she just says she's been too busy or tired. Well that may be the case and her career is important to her which is fine but what is not fine is to neglect the person you love. My suggestion is this, harsh as it seems, don't contact her for a while, see how long it takes for her to miss you... Go out with your friends and have a life don't wait around for her as she certainly isn't doing that for you. If my intuition is correct I think that she'll wonder what on earth is going on and be the first to ask! And if she doesn't time to realise that you just aren't that important to her as you thought you were. And only you can decide what to do with that information. Personally this happened to me, was patient for a while then thought nah I'm offski... Life's too short to not be important enough to be given some time and attention to. And look I survived!