I do it too babes. We're not alone. Sometimes, like you, i do it for no reason. My therapist and i have both agreed that I'm very fidgety, and i have been ever since we started out sessions. We both think it is a means of fidgeting for no reason. I have ADHD and cutting is something i started a long time ago. I didn't do it for a while, but i started again. Since it's addictive, when i need to fidget, i do something that feels good. For some people, its squeezing a ball, others its brushing hair. When people fidget, they tend to choose something that feels good. Cutting is an addiction, just like any other thing can be. Ive started to doodle and draw/colour when i feel he need, and I've started to make friendship bracelets. i tried the squishy ball and silly putty, but those things didn't work. It takes time. Some of my friends have cut too, and really, the only thing that works is finding something else, having supportive friends you can talk to, and time. Whenever i feel like I'm going to cut, i draw or make a bracelet. When I'm walking, since i can draw or make things, i hold a piece of string in my hands and tie little knots.
When it feels like no one understands sometimes, and i know this is sad, talking or blogging about these things with people you don't know helps.
I hope this helps,