Session id not unique

i have multiple database and a single asp.net 3.5 web application host on iis 7 . how to manage seeion id ?
i am facing some problem database switching ?
example :

i have 2 database :
1. db1 <-- user -- sachin (sql user)
2. db2 <-- user -- jigar (sql user)


if i have enter on application by user sachin on database db1. it will work finely ........... but anther user jigar enter on application by user sachin on database db2.
then first user sachin will be switching on db2.(or connection string are change. i have create dynamic connection string)

plz help me