How can I stop stressing from no reason? I know I have nothing to worry about but my brain thinks otherwise

Skills n techniques. Some simple anxiety techniques practiced regularly can be helpful. There r even apps for you phone such as tactical breather that can help teach breathing relaxation techniques. For other strategies see our stress articles and tips at: http://cpancf.Com/articles_tips_archives.Asp if need more see a clinical psychologist familiar with health psychology.
Just be present. Instead of trying to stop feeling stressed - just be present with your stress and see what you find out.
Remain activity. Activity and playing the good brain movie will help reduce worrying. If your brain is concerned about a bad event occurring, you can play an alternative movie where a more realistic good event occurs.