Sounds like teeth to me.
And I do agree that you may want to start working towards getting him to self soothe. But hard teething may not be the best time to start!
My LO still nurses before naps usually, but not to sleep. He's still awake when I lay him down. He sometimes fusses and cries even, but now that I have been consistent with it, he is going down typically quite quickly.
If it's teething, which it sounds like it is (messes up my LO's naps, as well), there isn't a whole lot you can do. Just try whatever you can to get him a nap. At this point, since my LO is already adjusted to our routine of me laying him down awake, I will let him cry some. But I make sure if it's really bad that I give him something for the discomfort first, like a homeopathic teething remedy.
Hope your LO gets more rest soon!