Would this be workplace descrimination?

I work in a doctors office and my office manager and I had ed heads recently and now I need to know if this is considered descrimination. I was off sick last week with the flu. I went to the doctor the first day that I was home and the doctor said that I should be off work for the remainder of the week. I felt terrible because we were short staffed already as it was, but I didn't want to put our patients or the other staff at risk. The office manager became frantic and making me feel guilty for being off stated that she wanted me to be back to work earlier than doctors orders. Me, not having my witts about me made a statement that I wouldn't have if I hadn't been at home with 101 degree fever and said what am I supposed to do and I did use profanity which I don't usually do in my normal healthy state of mind. When I returned to work I was welcomed by my office manager stating that I had been written up for inappropriate behavior. Ok fine I did act out of character whatever. But just a couple days later another employee went into the office managers office was yelling to where I could here her from my workstation which is out two doors around a corner and down a short hall and made a threat to the office manager and used the F word. No disciplinary action was taken on this employee and if anything was treated even better through the day than usual. How would you say I should react to this?