try to make a pattern in username and password like
my name is manish and i cant get manish for all site

use
manish_yahoo
manish_google
manish_aol
this is just example but you can find unique name then all site name

and in password what you can do is
same password and different site name like
my password is Swayam1$
Swayam1$Yahoo
Swayam1$Google
etc…

this will help you to remember things like username and password