Mine is the same age and doing the same thing for the last four or five weeks or so. It started off with his second molars, but I don't think these are too bad now. He is waking and wanting to come in my bed.
My hunch is that he is ready to drop his nap. This morning he woke at 6.10am and came in my bed (I suppose that does count as sleeping through, I guess). He then had 20 mins in the car at about 11, then no more naps till bed at 7.45pm. He was fine and certainly not overtired. Will be interesting to see how he sleeps tonight!
I am also experimenting with making sure he gets plenty of time outside and to run about - I am sure more natural light helps them sleep better. Today instead of pushing him about town in his buggy I ditched the buggy and let him walk. He was chuffed about that, and also I didn't put him in a highchair in the cafe but in a proper chair.
I'm also thinking of moving him to a bed. We were reading "Peepo" and he was pointing to the sides of the baby's cot in the book and saying "uh-oh, a gate" (uh-oh is what he says when something is wrong). So I am also thinking maybe he really isn't that keen on his cot anymore (though he does settle fine at bedtime, its just when he wakes up!)
He is still in an 18mth-3 year sleeping bag but since he is hugely tall for his age I also think he can't be that comfy as he has little room in it!
My gut feeling is that he is in a transition from younger toddler (cot, buggy, naps, sleeping bags, nappies) to older toddler (no naps, potty trained, no buggy, big boy bed).
I remember from my DD that this transition phase messed everything up a bit too.