I have noticed in the past that the bone along the back of head seems strange to me it hollows in a lot. The problem I have had from this has been many headaches. At the moment behind my right ear the bone is much bigger than on the left side and lately gets sore. I have seen my GP and she has referred me for a ultrasound as she said it should not be like this. She said it could be a cyst but I don't think so. I awaiting appointment but I am concerned. Could it be serious

If I were pressed to comment, I would agree that it could be a cyst. A cyst is more common and more plausible then random bone growth.

If it is a cyst, it will not be serious, it would be drained and stitched. If it is something else, then I would await your doctor's analysis of the growth. A side note, don't listen to what the ultrasound techs say. They know a lot, but a lot of their diagnosing is based upon experience and NOT training. It is easy for them to innocently give misinformation that could cause you to worry.

Wait until you're diagnosed by a medical professional.

If your doctor has referred you for an ultrasound, and said IT SHOULD NOT BE LIKE THIS, then I would follow her advise and do what you can to have it properly diagnosed. How do you think we can diagnose you one line? No, not at all. We don't know your medical history. Please have the ultrasound to appease your worry, and if it is serious, then go on from there to.

Of course waiting for a test is worrying.
But tickle is right - going online is the last thing you should be doing!
Use common sense. If you get a fever or any unusual symptoms, just call your doctor.