Yes, it is self harm..And if not controlled it might lead to worse,so you need to take it seriously.. I used to do that too, when I was angry and couldnt take it out on anything else.. But everybody has different reasons to do it, you have one too. If you harm yourself, you definitely have a reason for it, even if you dont know what it is..
Trying to stop is really hard, especially if you dont get help from a professional. You need to get help from someone, not because there is something wrong with you, but because you need knowledge about yourself and the reasons that push you to do this..
If you try to stop scratching without understanding the underlying reason, it can be a temporary solution.. Therapy helps, trust me.
I hope you will be better soon, wish you all the luck <3