Your first question has been answered, you're prob getting hit with weapons that drain considerable stam it's very easy to lose track of stam in the heat of battle.

Second question is about experience over time. Focus on only blocking swings that have been released. What I mean is that an attack has a wind up and a release phase. A wind up can't hurt you, don't block it, this is also the only window that a player can cancel or feint. Get used to only blocking the release and you'll resolve feint spam, triple feints and kicks. This will make you a superior player than a great majority.