Ummm... We are in justhost, I don't know how is that relevant, but is good to say it...

Anyhow, I don't really know how is it that the host only allows X connection for a user, this connections are for the time you are in their host?

the "x" connections doesn't mean the number of users on your site but more the number of calls per user to the database, as Lynne says, on shared hosting this is usually very limited, they do this so that they can oversell their resources, ask them to raise the number of max connections. You may find that they will refuse unless you upgrade your account.