What can I do if I did not have a patent but I shared (wrote down my plan) my idea with someone and they stole it?

If you came up with an idea and some third person stole your idea and is now reaping the financial benefits of the concerpt that you came up with, you have the possibility of bringing a common law action for misappropriation of property as to that person. Whether the facts of the situation that you are writing about warrant the filing of a lawsuit is an unknown at this point since your question is somewhat sketchy.

I recommend that you consult further with a business attorney to see if there is a factual and legal basis for you to bring a legal action against the person who took your idea for misappropriation.