Hi Izzzy and welcome to the forum.
It's a pretty broad brush stroke you're painting there but I'll throw this out there for you to consider...
If you can afford, in both time and money, to take some classes... That'd be your best bet. The classes will help keep you on track and push you forward. If you start out with an entry level physics class you can see how it goes and your professor can help point you in the right direction far as any future classes or suggested reading. If you'd rather go it on your own then take a look around a local college book store and grab a book or two. Most local schools will have a used book store nearby which could save you a good bit of money.