Github Pages, CNAME record, SSL certificates on a custom domain

I am trying to create a Github page pointing to a registered domain name. For example:

• example.com -> Github Pages
• test.example.com -> self-hosted web server

So I have created a couple of different A-records for example.com to point to the IP addresses provided by Github and so far the redirection is working. My problem is that I cannot really create a CNAME record pointing to a different IP, I need to use a domain name, but then it won't work.

I also would like to create Github Pages for all my projects. For example, I want:

• example.com/project_1
• example.com/project_2
• example.com/project_3

If I enable the Github Pages for them, I cannot have the same custom domain (example.com) set on all of them. How can I achieve this, do I need to create a new repo, dedicated to the Github Pages and then create the whole website in this repo?