Keyboard keeps switching to Japanese layout?

I have a 2015 MacBook Air. Basically, despite my keyboard being an American layout, it keeps switching back to a Japanese layout. I've used Japanese layouts in the past when I studying the language, now it keeps doing it without me being the one to change it. I think it started when I plugged in an external keyboard (custom-made), but now it's doing it with my internal one as well. I've tried restarting it, shutting it down, and deleting the Japanese layout altogether, but nothing works. I'll shut down the computer, turn it on, and go to system preferences>keyboard; it will look like it's back to a normal American layout but I'll press a key and it will automatically change back to a Japanese layout, again both with the external AND internal one. My external one, btw, is still an American layout and is not even Japanese-made. Has anyone else run into this issue?