Hi Alyx,
I am not a doctor so my thoughts here could be completely wrong. But, it sounds like you might be experiencing Excoriation (it is also called Dermatillomania) which makes you want to scratch at your skin. I think it is sometimes brought on from anxiety. I don't have the disorder but have another skin disorder caused by anxiety.

To find out about Excoriation, here is a few links I found :
Skin Picking Disorder (Excoriation): Symptoms, Treatment, and Causes
The ABC's of Dermatillomania / Skin Picking Disorder

You could talk with your parents and tell them you want to see a therapist about it.