Website login

I have a domain name registered on some domain server. Sometime back, I took help from 3rd party to host website on this domain name. I have lost contact with that guy.
Now, I want to find out which domain server this is registered on, I have login details like login Id and passwd. Also currently my domain is working and getting directed to some web pages. In settings I tried to find out where this forwarding is done, but I am not able to figure it out. I looked into settings related to domain forwarding, A records. But could not figure out where it is getting directed to, and from where html pages are loaded.
I wanted map one IP addr to one subdomain, to I updated A record, but it didn't helped.
So in short, I am looking for answers to following questions
- which domain name server, my domain name is registered on to. From login URL I could not figure it out well, as url is going to some basic webpage without nice banners. Need to find proper login URL.
- find out where domain name is getting redirected. Find out where are HTML pages hosted on.
- help me to add sub domain and map it to custom IP address.
thanks for help in advance. I know answers should be straight forward, but going to URL, I am not able to figure it out well.