Never done cocaine or been around it but I did a pre-meps drugtest why did I get a positive?

For my weight issue I took these water pills called H2O Lean that day and a body cleanse drink a week prior. I dunno if those had anything to do with a false faint positive or not? If you have any idea why it would have happened or how I can prevent it for tomorrow please help! Also will senna pills affect it as well?