Better than cleaning the blades, use a new one each time.
When you say you're "scratching" it, is this because you're using a shitty disposable razor which does frustratingly little? Or is it that this is sufficient to achieve the desired effect? Is it the action and sensation that you want? Is it an external expression of your emotional pain? Do you want to gain the attention of someone (perhaps a parent) that you feel is neglectful (it's nothing to be ashamed of)? But it's important to be honest with yourself about the motivation for doing this.
As has been said, hygiene is crucial. Wash your skin beforehand, use new blades where possible (boiling them and using a disinfectant are alternative measures) and thoroughly wash the area afterwards.
I just always had a fascination with the blood. I would collect it in small bottles from an early age, just to see what happens to it with time. I find keeping a picture of a nice, gruesome wound useful and it tends to satisfy the urge.