often purging is not about weight, more about a sense of control / out of control of trying to "get rid of" something, for me usually something emotional, I feel good when i'm empty,
You said
I don't think it's a problem because i've only done it three times i just need advice
I'd be careful, it could be the beginning to something more serious. Everybody starts like that. I thought that i could just do it to make myself feel better when i couldn't control my emotions. It became something that at times i do 5 or 6 times a day and i can't control. Nip it in the bud while you still can. If there are other difficult things in your life seek some help, or talk to someone if you have someone near that you trust.
You can talk here if you want to expand on what you said,
Take care