My 17 month old naps for 50 mins to 1 hr each day.

I'm really struggling with naps. LO is really cranky by 11am and it doesn't seem possible to extend it anymore. He only naps for 50 mins to 1hr, but will be rubbing his eyes and showing tired signs a few hours after. He won't take a second nap if I Give him an earlier morning nap.

What do you think the problem might be? What would you do?