Why is it that sometimes I sign in and stay signed in for days or weeks, other times I have to sign in each day, is it an age thing to tax us oldies?? to make us think more often???? so many questions

Usually keeping you logged in is a very small piece of code called a cookie, so deleting cookies will leave you logged out, changing settings in your web browser to delete cookies at the end of a session will do the same.
Using more than one web browser where one of them has that setting will do it every time you use that browser, and refusing to accept cookies will also do it

Rules were changed a while back about automatically forcing cookies onto computers when you opened a new website so often now you will see a box asking if you want to accept cookies.

I like cookies, where do I collect them????????