I'm a little late on the response train.
But I have a lot of info on the kin communities, since I spend a lot of time in them, so I thought I'd ramble on with an answer of my own anyway.
If you feel that you're soul isn't human, and it's a feeling you've had for a long time that you can't get rid of, you're most likely on the right track by looking into Otherkin.
Have you looked into the mythology and lore of fairies? Perhaps delving into their world, stories and customs would help you see if there's anything there that's familiar to you. The more you search, the more clues you'll find.
Also, getting onto Otherkin forums would probably help you figuring thing out. If you find people who can give you the information you need, then that's great! If you decide that you're probably not Otherkin after all, you can just move on to something else. No harm done.
That's what self exploration is all about.
I don't know if you're still looking into all this, but if you are, you can pm me if you'd like. I'd love to talk to you more.