My DS just turned 3 a few weeks ago and we had awful sleep from 34-36 months ,no amount of routine tweaking worked we had terribly long repeated night wakings and we were all exhausted as I'm now 28 weeks pregnant! He would tell me he wasn't tired and didn't want to sleep but then dark circles under his eyes said different!
My point is it looks like it was developmental, his language, conversation and imagination have all come on immensely, I don't know where he gets it all from, but he has us laughing at his grown up ness.
We had dropped his nap, completely back in feb but have had to re-instate a 45 minute nap as he seems to need it and is easier we had to give at least 6hr A to bed, so earlier nap is working for now with BT 7.30 we're getting 12 hrs in total over 24hrs
So hang in there, hopefully it passes a little quicker for you!