I wanna cut but I just can't

I wanna cut so bad but after a couple minutes I just keep forgetting that I wanted to relapse. I know, cutting IS bad and I even have timer and I report to me every time I relapse but I started cutting with a dull knife (now, I have razor blades) and it was hurting when I went to the blood so I think my brain just marked both: "cutting = hurts" and "cutting = good". I know it's very strange but I just can't, this shit feels so bad when I clean for like over 3 weeks (like right now) and any little thing can make me into state of a suicide attempt.. so.. had anyone smth like that or so and have "fixed" that ? (Just for admins: cutting is really bad for a lot of reasons but here I just can't cut when I want it the most, even before the exams and on exams I feel like I want it so bad that I wanna just start cutting my arm so I wanna solve that so I can control my urges better)