He may be transitioning to less day sleep.... does he still have a nap earlier in the day? Both my kids have done the same as Charlotte's at around the same age.
If he's not sleeping, just get him up and do something else. It's the time of day when I tend to wear DD on my back if I need to get things done.

It is hard when they transition because there's often a period of time when they need more sleep, but just can't manage it. It'll pass, as with all things.

IT's also a common age for a spike in separation anxiety, which tends to last till 2~2.5.