Pretty sure the login thing is related to Obama's wiretaps, it only happens when there are threads with certain keywords such as Bigfoot, pizzagate or ball gaged gnomes being reamed out by Ronald McDonald.
Cookies are stored on your computer by websites you visit and contain information such as site preferences or login status. First, make sure you arent using IE, use Chrome or Firefox browsers. if you are using those browsers already, clear the cache. Make sure you select "keep me logged in" when you log in here on PP, and ensure that in your browser cookie settings, they are set to always accept third party cookies and keep them until they expire.
I use IE, Safari and Chrome, each one logs me out even though I check the stay logged in box, IE on my laptop logs me out the second I click on a forum. The others require me to log in far too often. Other sites will keep me logged in for years, even if I don't visit often.
This started a while ago, and is a bug somewhere that hasn't been fixed. Usually I log on, and it just stays that way for a day, or half a day...I don't have to re-login frequently.