When I go workout, I feel fine, but not energetic. So I start working out and after a little while, I start feeling tired. I yawn a lot and just don't feel like working out. It's like my energy level is really low. And if I try to force it, like forcing pull ups for example, my arms kinda feel like they're shaking. Like when I pull up it's not a smooth motion, it's kinda jerky feeling. Anyone know what causes this? And how can I get more energetic for my workouts? Maybe doing some running before lifting?