You really need some legal counsel on this. Sit down and write down the entire series of events. If you don't have any cash for an attorney, check for one that works on contingency or look to see if there are any free legal aid agencies in your area who can let you know if you may have a case against your employer.
I am not one who is usually in favor of pursuing lawsuits, but if your boss put you in a situation that was forcing you to quit because of health reasons I believe you should go after them.