So I've been using Corel Painter 2015. I chose to stick with this cause the selection of brush that it offers. SO much of it and I love it. That's the reason why I opted to use it instead of Sai, Photoshop or Clip Studio Paint. However, as I'm using it, I realize it's lacking and frankly too much features that I have no idea to use. What it lacks? I can't even find a shape tool to make a triangle. So I need suggestion on what software to use.

Corel also makes Paint Shop Pro, which (as a non-artist) I like.

You ought to download the free trial and see if it has what you need (it can draw basic polygons).

X8 is the current version, and is on sale for $56 on the Corel website. (Note: You don't need 'Ultimate', they just bundle some resources and an effect or two with it, and charge $15 more )

X7 is what I'm using, and costs $26 on Amazon for the downloadable version.

If you wait until Black Friday or December in general, I bet the newer X8 would be $30 or so on Amazon Goldbox deals - it was last year.

But definitely try the free trial first.

[Edit:] To be clear, Paint Shop Pro won't replace your current program. I'm saying Paint Shop Pro might supplement it, if you want to use both.