Login screen accessible everywhere

Hello. I recently just got a VPS and i decided to install GitLab. I got it installed and everything seems to be working fine. I had a smaller website and i transferred it over to the VPS. It had some sub domains for a forum and what not. However after I installed GitLab no matter what URL i type it always shows me the login screen for GitLab. So mydomain.com shows the login screen as well as gitlab.mydomain.com, forum.mydomain.com, cloud.mydomain.com etc.

How do i go about changing that so ONLY gitlab.mydomain.com shows the login? I would like to have other things on my webserver as well.

I don’t know if it matters but my VPS is through a company called ASmallOrange. I am relatively new to web servers and such so i’m sort of lost on what to do. Any help on what to do or where to start would be much appreciated!