Multiple Organizations under one Zoho Account?

Multiple Organizations under one Zoho Account?

I have 3 different companies/entities for which I have set up separate Zoho accounts:
1) NuInvest (own domain)
2) ISLSP (own domain)
3) Gpolzer (personal no domain)

Questions: should I have set up one Zoho account and established multiple organizations with different domains.  It is becoming difficult to log in and out and am trying to consolidate under one 'umbrella' account if possible.  Thank you.
George