I asked for a raise, was denied, then missed work (bronchitis.) I was then asked to resign. What can I do?

I asked for a raise, and was denied. I then missed a few days of work due t bronchitis (I have doctors notes and prescriptions.) When I came back to work today, I was asked to resign because "it's not a good fit." What should I do? Is there any legal recourse available to me? I feel like it was retribution for asking for a raise.