I love being locked in bathrooms, it triggers these feeling of wanting to slice myself, it feels so good, massivly orgasmic, what to do?

You could poop outside.

you can visit a psychologist or councillor for help and yes you should first learn to control your feelings

Sweetheart, You have been abused by a narcissist. Cutting and things like anorexia come from long term narcissistic abuse in childhood. Usually, the parents are the narcissist. Learn who the narcissist is and get them out of your life and you will start to feel better. It's no overnight cure but in due time you will begin to get better. You can then become the person you were truly meant to be. Study your head off about narcissism this is so you can spot them in the future. Because you have been victimized before by one you have a big red target on your head that the others can spot now too. Look you can't avoid bathrooms. But you can avoid the people who gave you those feelings in the first place. They made you feel like you aren't good enough. I am telling you that you are good enough even broken and abused YOU are GOOD ENOUGH!!

You need to speak to a professional. There is no good reason as to why this is happening. Professionals are there for a reason, to help. 

You have an Addiction.  Instead, trust Jesus Christ and receive comfort from Him.  Repeat:  "Spirit of Addiction, leave me know in the name of Jesus."