I recently decided to learn musical theory. Browsing through this site has been very helpful so far and I thank everyone here for being so patient with me and my stupid questions.
I have been playing guitar for a long time but learned by ear. Wrote tons of riff.
The more I learn about music theory, the more I understand what my music is built on. Found out that I often change key within the same songs, and sometimes change scale. I wrote a song where I change key 4 times and played on 2 different scales. The song is not very long, around 5 minutes. I was wondering if its normal to change key and scales so often. Is there something wrong with my composition style?
There's such a huge range of different musical styles, that the concept of "normal" is pretty arbitrary. It's probably not normal for top-40 pop music, say, but it's not out of the ordinary for jazz or prog, and when you start to get into things like 12-tone theory in classical sometimes you don't even really truly have a "key" to begin with.
The litmus test is, "does it sound 'natural' to your ears" allowing for the possibility that sometimes NOT sounding natural is also the intended effect and that's cool too. If you're creatiing the sound you're going for, then sure.
Though, IMO this points to another really good reason to learn music theory - if you're going to start to venture outside "standard" key and tonality structures, you should probably know one that you ARE doing so, and two how it's all holding together and what's making it gel.