The bar right under health in the fatigue bar. It starts to fill up with green as you perform actions that make you tired (working, fighting, traveling, etc.) and can be recovered by sleeping, bathing, and a few other means. Being fatigued grants you a debuff during combat, decreases the effectiveness of your spells, and may prevent you from taking certain actions like working. If you fill the bar completely you can become exhausted, which is an even more severe form of fatigue, so make sure you rest when needed.
The dots under the fatigue bar are blood droplets. You'll find out what they do as you progress in the game, but I don't want to spoil it as it's a cool mechanic to discover on your own and the game will tell you how to use it when you get to that point.