Will I be doing the right thing?

Hi guy's and girls, Happy new year to you all, hope everyone had a belter!

I'm not having such a great start to the new year unfortuantly. I've been with my gf for just over 3 months now, was going very well, spent a lot of time together at christmas and she met my family etc. Got on really well in fact and also are planning a holiday together. My problem is that since new years eve she has been very off with me, we woke up together new years day, think I annoyed her as she wanted to carry on sleeping so I left. Anyway, since then she hasn't called, sent me a dry text messege last night and then called her and she never called back.

I've also emailed her at work, just saying is there anything wrong? She just said too busy to email at the moment, said she's miserable and will email me later. I just can't understand it. I know i'm paranoid at times but why should I have to put up with this? If she sometimes asks me is there anything wrong etc I put her straight straight away so she doesn't ponder it.

Bascially i'm very much into this girl and want to be with her but this is the second time she's done this to me and I feel like shit all day, I think this is the last straw and I will be brave and say thats it and call it a day, f**cking well sad about it but what can you do?

Any advice or suggestions??

Thanks