My 17-month-old is in a similar situation. I know his 2-year molars are bothering him, since he's been drooling and chewing on his hands the last few weeks. So even if you can't see any signs of the teeth, that may be a culprit. Otherwise, a few things I've thought might be my son's problems are dry air, not enough daytime exercise, tummy ache, and bad dreams (adults and kids have them, why not toddlers?) I am personally against CIO, since the child is crying for a reason and parents should try to help them, not ignore them. Especially if the crying lasts for 2 hours it sounds like he needs something (maybe a drink of water? Some cuddling?). However, you know your child best, and can tell when he's really needing something or just trying to get his way.
Also after reading this board and other places, I am starting to realize that there is no magic age when kids "should" be sleeping through the night. I think it is a developmental thing which can be influenced by all sorts of other stuff. And it definitely changes when there are other big things going on (teething, developmental milestones, daytime circumstances). Adults don't always sleep through the night -- why should we expect kids to do that all the time? The best we can do is help the process as much as possible.
Hopefully this is just a short stage and all of you will get some better sleep soon! Good luck!