Sounds like a growth spurt. I know you are breastfeeding, but are you also doing solids. Might be time to introduce a 2nd meal (of solids) if you aren't already doing one. If you think it's a growth spurt or he's just plain hungry, you've got to figure out a way to add more calories. WHen he cries at night, what do you do....do you go straight in to him or do you wait a bit? Sometimes, if I don't go in to Z right away (only when he's just fussing, I always go straight in if he's really crying) he'll settle himself. WHen I do go into him, I just lay him back down as many times as it takes (PU/PD) or leave my hand on his back so he knows I'm still there (I don't pat or anything). When he does this once in a while, as long as I stay consistent with this, these nightwakings only last a night or two.
As for the short afternoon nap, both my kids did that for a while. Can you try to distract him in the afternoon before his naptime so you can extend his awake time with hopes of extending that nap??
I really hope you decide not to do CIO. Even if you just sit in his room with him while he cries, he needs to know you are there.
{{{HUGS}}} I know the nightwakings are hard, but all the work is worth it.