I cut myself at work a few times last year
I'm sorry that's awful, why do you cut yourself at work?
I've been very frustrated and stressed out at the same time
It sounds like you are doing it on purpose. You should seek mental help therapy to deal with your stress and frustrations.
I'm very strong and I don't need that shit.
There's nothing wrong with going to therapy for such issues, tons of people do it all the time.