What can I do?

First I would like to say, I live in PA and work in DE as an RN. I have just been faced with a difficult situation. I was asked to leave with the option of resigning. I worked there for a little over a year. An employee there was writing up documentation reminders by the dozen, not just on me, but other employees. I asked the other employees if they were getting pulled in to the office for these reminders. I asked 2-3 employees if they were getting reprimanded, and they said no. I was pulled in to the office for verbal warning. I then was told that this employee needed to stop this nonsense. So it stopped. So every little mistake I made, after this, I was being pulled in to the office. The DON would tell others about what I was doing, and telling them to ask me if I was having some kind of difficulties. She also told me that this environment may not be for me. She would also say your co-workers you are not doing your job. I believe then another 3-4 months went by and I recd a written warning on something that everyone else as well as myself,were responsible for. I was told that I could stay late and finish my work, but I would not get paid for it, the company does not like to pay overtime. So then another couple months went by and I recd my annual evaluation, which was not outstanding but good enough to get a raise. Meanwhile while I was getting written up, no one else was. I have notes from monthly meetings that were directed to all staff about the same thing I was doing, but they were not getting reprimanded. There are a few other items I could go in to but I need to get some information from this. Do I have case of Dafamation? Harrassment?