I hadn't changed any of my brush settings and midway through using it, it's changed itself and I can't fix it. I usually like using the hard round brush but now it's stuck looking like I'm using a spray can line and I don't need that. It now doesn't matter how I change the brush tool, it's stuck on this one setting.
I've tried resetting all of my tools and restarting my computer and it still is broken and I can't find anything else to try. Any help is greatly appreciated
Check the options bar and change the Blending mode to Normal. It may be on Dissolve. If you don't see it, then show a screen shot of your options bar.
... midway through using it, it's changed itself
The shortcut to change to Dissolve is Shift+Alt+I, which you may have done accidentally when you were trying to do something else. It will change the Layer if you are on the Move tool or the Brush if you are on the Brush tool. See a complete list of shortcuts for Blending modes in this list from Jesús Ramirez:
Can you post screenshot with entire window and Layers panel visible?
Your layer is set to dissolve mode
As already stated by @davescm change blend mode for selected layer back to Normal. Use first drop down list on the left side above selected layer in the Layers panel to set Normal blend mode (currently is set to Dissolve).