What you need is to stop thinking about everything at once. You could suffer from anxiety, and therapy could help you focus.
However, meditation helps my friend focus when he over thinks about things. He focuses on one single thing (a rock, his hand, even a painting he saw as a kid). He lets that one thing fill him, fill his mind like water in a cup. He also uses deep breathing exercises to increase oxygen to the brain, which helps in concentration. It's why you yawn.
Meditation only works if you have some serious self discipline. I recommend deep breathing while listening to calming music. Even if what calms you down consists of screeching guitars and throaty vocals.
If you can't think of what calms you, then use that as your first focus. You do not always have to use the same focus..