Hey there,
I agree with everyone here, I don't think this is cause to panic. Birth control messes with your hormones and causes pregnancy-like side-effects. She would definitely be feeling those since she just started them. Plus, she wouldn't be feelings pregnancy signs until later. Try getting a pregnancy test just in case though, if anything it should calm down any panic you or your girlfriend might be feeling. Also, I would recommend using condoms if you don't already until she's gone through a full menstrual cycle on the pill just to be safe.
I hope this helped
