Eagle Vision and glyphs Help!

Ok i don't know if anyone will be able to help or not because i don't really know why, but Eagle Vision has quit working. I'm a good ways through the game and have used it. i didn't play the game for awhile and went to go back to it but for some reason i can't get eagle vision to work at all. Its not the button because the triangle button works fine for everything else except i can't use eagle vision. Is this a glitch or is there a reason why it suddenly quit working that i missed? And if you know why its not working, is there a way to fix it? I'd rather not have to start all over. Also i'm having trouble syncing the glyphs. I figured that has to do with eagle vision not working also. Please help me if you can! I've been trying to find answers, but no luck so far.