Grounds of law suit for name defamation.

Please help, for the past year I have been labeled as a drug user by some of my senior peers. It started off from one peer and eventually got around to the rest eventually leading to my boss. This accusation is based off no facts, proof, or witnesses. I was thrown off at first, I didn’t think much of it at the beginning. I just thought they were jokeing and just hazing. But I noticed I started being treated differently and I didn’t understand why when i had a good relationship with everyone in my first 2 years of employment. Then I started to put the pieces together, and it made sense what was going on. I recall speaking to one employee about finally reaching my goal of making 6figure income, i did it with now malicious intent. I assumed he was already making that amount if not more seeing he was a senior employee. But I started to see anything that could be said to discredit me was being said after this statement being made about my income. Yesterday I got written up for attendance issues as I was going through personal issues with my wife. But I was automatically said to be negligible in communication with my supervisor and even on days I did communicate and have text and call logs to show. I was still said to not have communicated with my employer and grounds for termination. I was really thrown off by this as I couldn’t understand even when I did my part. Granted there was misscommunication but I owned up to everything That was my fault. But I will not take the blame for the things I didn’t do. So I was going to make an appointment with LabCorp and have a drug screening done and hand my employer the results along with my resignation. If proof is provided these accusations were made on opinions. And I have results that from LabCorp that prove i am drug free. Do I have enough ground to file for defamation of name by my employer and work peers?