I stole money from my employer during a mental break down, I confessed and told them I wanted to make it right and pay it back, this was about 3 months ago and I am now being accused of other things I did not do. They keep threatening they will put me in jail can they do that after 3 months?

"They", being the police? Perhaps. But, of course, they would have to charge you with some crime first.

If they want to talk to you some more, refuse to do so without first talking to an attorney. And, I hope you understand, an attorney must be provided to you if you cannot afford one.

No police are involved yet, just the threats from the employer
That I will go to jail, I have no money so getting a lawyer isn't something I can do right now

As AK said, if you cannot afford one, one will be provided for you.

Yes, depending on the amount stolen, it will be a misdemeanor or felony. So for from a year to several years, they can call the police and report it, and perhaps you will be arrested.

Why are you still working there, I can't understand why they keep you working, esp if they think you have done other thefts, something does not seem right, unless they are setting you up for a major crime down the road.