High haemoglobin?

Hi, I went to donate blood today but was refused on the basis that my haemoglobin count was too high. it was 18.1 (?) I'm male, 21, 6 foot, 73KG, caucasian, Irish (I don't live in a high altitude area). Otherwise seemingly healthy, no allergies apart from pollen.

Is this high? I'm going to see a doctor tomorrow but I'm wondering what are the implications of high haemoglobin. Also, my circulation is pretty bad and I'm often quite tired. Thanks!