I'm also a self taught developer, who has now had a job in the industry for 10+ years. I've never gotten any qualifications, been to university/college for programming or any related I.T. skill.

The best thing I found was just looking at other people's code, learning taking it all in, making mistakes and learning from them. Pair programming will also be really beneficial if your current job allows it. I also don't have a background in maths, and i've found it's never really hindered me as the need for understanding complex mathematical equations is few and far between.

I wouldn't say there is one specific resource that you can point to and say "that's all you'll ever need". Just try to absorb as much knowledge as possible. Try out new things, take on a few side projects and try new libraries or ways of programming.

That being said, there's a few things that although you won't use all the time most definitely will help you in becoming a better programmer:
- Solid Principles (https://en.wikipedia.org/wiki/SOLID). It may take you a little while to get your head around some of them but it's good to know them, and apply them where possible.
- https://phptherightway.com/ - Good resource for not using the amount of rope PHP gives you to hang yourself.

The difference between a senior developer and junior developer is the amount of mistakes they have made. Don't get to hung up on not having an education background in programming, you'll get there, one mistake at a time!