Tired toddler

My son just turned 17 months old. We have a scheduled bedtime from 7-7 and he is down to a single nap a day scheduled from 11-1.

He usually only sleeps until around 6am most mornings and his naps usually only last 50 minutes.

The problem is that in the mornings he gets spurts of energy and then has spurts of appearing tired and no energy. It is not an extreme tired where he is falling asleep while doing something though.

I am down to the conclusion that it is because of an overall lack of sleep. This is either because of too short a nap or because he isn't sleeping long enough at night.

If it is the latter then I believe it is due to sleep association where he associates waking up early with getting to come into our bed because that is what we have done for a long time. Once he is in our bed most mornings he will go back to sleep until 7am.

If the problem is his nap I'm not quite sure what to do.

Anyone else going through this or have experience with a tired toddler?