Emperor with no income

Hello, just got for the first time a empire. I started the Munchard start, and managed to get the britain empire.

But, when I died, then my son got the emperor title but no possesions... I had the primogeniture so I don't know what happened, but the case is without possessions I earn 0.1 gold/month, and I went from 7/7 possessions to 1/6.

What can I do in this situation? Is nonsense, as emperor I have less power and richness than my vassals that got a reign...