Custom namespace not found by Assembly-CSharp-firstpass,My custom namespace isn't found in Assembly-CSharp-firstpass using VSCode

I work using two namespaces: one that is game specific, and one that has utitlities that can be re-used by other games. I'm finding that my generic one is not being found by Assembly-CSharp-firstpass in VSCode. So, I lose all my intellisense, and I get lots of red error messages that are annoying.

The game compiles fine and runs as expected, but I want my intellisense working. I'm not sure how this firstpass project works. How can I make it so my namespace is found? ,Hi there,

I'm using VS Code with Unity 2017.3.0f3, and I'm finding that one of my custom namespaces isn't being found by CSharp. But, other namespaces from say a plugin, are found. When I run my app in the Unity Editor, everything works fine, so my namespace is eventually found when the project is built. But, for some reason, when working in VS Code I'm getting intellisense errors. It's annoying, and it's slowing me down, so I want to solve it.

I'm basically working with two namespaces: one that is game specific, and then I have a general one with utilities that are generic. It's this generic one that isn't found.
Any help is appreciated on how I can solve this.