I've been searching around for a while now, and can't seem to find any good answers, so here we are: 

I can't seem to access subclasses, feats, etc. for my own characters, much less have my players find them. I know I have all the books in my library, I know I'm subscribed at the ''share content'' tier, and I know I've turned on sharing. So why doesn't any of this show? 
Not the first time I've had this issue, but first time with books I myself own.
Help?

Make sure your Account Entitlements are in sync: (https://www.dndbeyond.com/account/marketplace), then turn content sharing for the campaign off and back on again.

Still isn't working. And now I have even fewer options for subclass

Are you using the website or app?

When you say you have those books “in your library,” do you mean you download them to the app, or that you have personally purchased them from this site?