Does your school allow you to go to college for Psychology? I have friends who are doing that and I think it could be a good option for you!
Crashing a language could be an option too, but if you don't speak any other than English/haven't studied any before it might be difficult. I crashed Higher Italian last year and found it quite good but I did it alongside Higher French (which I did at Nat 5 too).
Are there any other highers you can crash at your school? Maybe Higher Biology could be an option, it's mostly content based so Nat 5 knowledge isn't necessary, and you have previous science experience from Chemistry. Higher Mods or Geography could be an idea too.
Hope this helps!