I don't know what I did, but it's working now.
I'll try to recount what I did between posting this and right now:
-Messed with a lot of settings on my phone, but nothing major that I can remember. Just what apps can do what, changed some background app preferences, and I don't remember what else.
-Fearing a factory restore, I turned on photostream on my phone and initiated a new iCloud backup. Let it run and finish.
-I manually backed up all my photos
-Plugged my phone into iTunes, opened it and went to music. Noticed I had music waiting to sync, couldn't delete it or do anything else with it.
-I deauthorized and reauthorized my computer a few times.
-Clicked "Sync" at the bottom and it synced it all.
I can now add music to my phone no problem.
Thanks for your input.
A few things though: I have a PC and I had already restarted my computer a few times between the start of the problem and the solution.
It seems like the weird "delete your voice memos" fix did the trick, although idk how since I didn't choose to delete them. I was hoping to avoid that because I have a lot of voice memos, but they're backed up onto my computer and now my phone works so I guess I can't complain.
I tried all the above options without success.
What worked for me(ONLY IF YOU HAVE iTUNES MATCH) was simply going into my actual iPhone and just clicking the cloud icon next to the albums or songs that I wanted. You have to make sure that in the music settings on the phone itself that "show all music" is on.
For whatever reason I still can't drag and drop songs while on my actual MacBook into iTunes > iPhone but this was actually better for me because I don't need my laptop to manage my music really(aside from playlists though, that's another issue so Apple definitely needs to fix this drag and drop issue!).
I've spent the last two hours trying to get some new mp3's onto my iPhone 4 from iTunes!
It just won't work no matter what I try!
I pay for Match but it's pot luck whether or not it decides to sync your music between devices in a timely manner. Normally it takes a few hours before my song finally shows up on my iPhone!
That's absolutely no good!!
I make music and constantly have fresh, new tunes that I need to put on my iPhone to listen to in my car, on a walk, in the shower, on a stereo system, etc, etc.
I don't want to be waiting a random number of hours before I can hear my tunes!!
I turned off Match so I could add tunes to my iPhone manually, but every time I drag any songs over to my phone, iTunes says "preparing to update" and then gives up after a few minutes, having tranferred absolutely nothing over to my iPhone!!
I'm seriously pulling my hair out here!!
It's so pathetic that I can't help but laugh every time Apple's products fail with such simple, basic tasks. It's ridiculous and farcical. A joke.