It could be a couple of things, itching is really common in pregnancy.
At your stage, i'd say it's the increace of blood volume- I know that sounds crazy, but as soon as you are pregnant, you produce like, litres of new blood for the baby and the placenta, the increased circulation of blood can cause itching.
Later on, as you start to get bigger, the skin on your stomach will probably itch- this is from the skin stretching.
I don't think there's very much you can do about it at the moment- maybe ask your doctor, see if he has any suggestions- I tyhink it just goes away by itself, or maybe you get used to it- sorry that's not much help. !!!!!!
Ask the doc if it's driving you crazy.