They're unread posts since you last visited, so if it thinks you were just here, it would say "nothing new in the last 5 minutes" or however recently the board thinks you were here. It could be an issue with your cookies. Do you close the window when you're done or just the tab? What browser are you using?
To recap: the government is continuing to play silly buggers with our futures, some of us think Brits are bonkers, some of us think Americans are bonkers, a newbie asked a question someone answered for a different newbie yesterday, and there are a lot of comments proving that we're the best community online anywhere.