When did it start?
Can you tell me why you think she is acting this way?
What are you ages?
How long have you been together?
Thank you for that additional info. It's a little difficult to ascertain which one of you may be at fault here or if either of you are at fault....let me explain. On one hand, if she says that she is just tired, then maybe she is just tired. If you persist in asking and asking again and again, and she really is just tires, it makes you look unstable. If she is hiding something, then you could be picking up on that and it's driving you to be persistent. There is also a third possibility, that there isn't anything wrong, but that its her personality to keep you on your toes and you are responding to that, basically meaning that your personalities are clashing. Sometimes when a person wants attention, they act a little funny, or they say, I'm tired, or I have a headache, to get that little extra attention. The same goes for someone who is cold one minute and warm the next, it can be attention seeking behavior. Theres always the possibility that there's another issue (or person) involved. That she has something going on in her life, or someone else in her life and thats making it hard for her to deal with things, hence the stress and strange behavior. There's really no way to know unless she is straight out with you. Then again, it could be nothing, but being tired, and having a headache. You have to look at your relationship with her and balance it out based on what you know about her, and how your relationship has gone.
I think that letting her reach out to you like you have has been good, it kind of puts the ball in her court. You can also make sure that when you are on the phone, that you get off the phone first, this kind of puts her off balance, just enough to think about why you're so busy, and perhaps want to talk to you more. I welcome your thoughts, let me know if you want to talk more or have any questions about what I've said.