I'm 20 years old, I have been laying down to go to bed and my mind is raceing. Whats wrong, what do I do?

Hope is alive. Racing thoughts can be due to many causes including: medications or over the counter remedies (even coffee or nicotine), anxiety, hypomania, medical conditions (hyperthyroidism), and substance abuse. Investigating the potential causes with your md would be a good start. Numerous prescription medications can slow racing and provide you restorative sleep.
Mind racing. This can be something simple or serious. Just having a lot to think about and unable to make decisions can be cause. Write down your thoughts, talk to friends and family. If you start having more symptoms see a professional for an evaluation.
That depends. The question is why is your mind racing when you lay down for sleep? That answer can come from a thorough psychiatric evlauation. Then you and your doc can put together a treatment plan to get you better.